diff --git a/Dockerfile.dev b/Dockerfile.dev
index bdb0588..989078e 100644
--- a/Dockerfile.dev
+++ b/Dockerfile.dev
@@ -148,8 +148,5 @@ RUN cd test && \
 
 RUN cd test && \
     for arch in $TOOLCHAIN_ARCHS; do \
-        case $arch in
-        arm64ec) continue ;;
-        esac
         cp $TOOLCHAIN_PREFIX/$arch-w64-mingw32/bin/*.dll $arch || exit 1; \
     done
diff --git a/build-compiler-rt.sh b/build-compiler-rt.sh
index b56aa48..98b424c 100755
--- a/build-compiler-rt.sh
+++ b/build-compiler-rt.sh
@@ -134,26 +134,7 @@ if [ -n "$NATIVE" ]; then
     exit 0
 fi
 
-ARM64X_FLAGS=""
-if [ -z "$SANITIZERS" ]; then
-    for arch in $ARCHS; do
-        case $arch in
-        arm64ec) ARM64X_FLAGS="-marm64x" ;;
-        esac
-    done
-fi
-
 for arch in $ARCHS; do
-    FLAGS=""
-    case $arch in
-    aarch64)
-        FLAGS="$ARM64X_FLAGS"
-        ;;
-    arm64ec)
-        continue
-        ;;
-    esac
-
     [ -z "$CLEAN" ] || rm -rf build-$arch$BUILD_SUFFIX
     mkdir -p build-$arch$BUILD_SUFFIX
     cd build-$arch$BUILD_SUFFIX
@@ -179,12 +160,17 @@ for arch in $ARCHS; do
         -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY \
         -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY \
         -DSANITIZER_CXX_ABI=libc++ \
-        -DCMAKE_C_FLAGS_INIT="$CFGUARD_CFLAGS $FLAGS" \
-        -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS $FLAGS" \
-        -DCMAKE_ASM_FLAGS_INIT="$FLAGS" \
+        -DCMAKE_C_FLAGS_INIT="$CFGUARD_CFLAGS" \
+        -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS" \
         $SRC_DIR
     cmake --build . ${CORES:+-j${CORES}}
 
+    # Skip install on arm64ec, we merge archives instead.
+    if [ "$arch" = "arm64ec" ]; then
+        cd ..
+        continue
+    fi
+
     cmake --install . --prefix "$INSTALL_PREFIX"
     mkdir -p "$PREFIX/$arch-w64-mingw32/bin"
     if [ -n "$SANITIZERS" ]; then
@@ -212,6 +198,20 @@ for arch in $ARCHS; do
     cd ..
 done
 
+# Clang expects the aarch64 compiler-rt name on ARM64EC. While this could be adjusted
+# in Clang, the current approach mirrors MSVC, where the core CRT is provided as
+# archives containing both EC and native support. Ideally, the LLVM build system would
+# handle this automatically, but for now we can merge it here.
+for arch in $ARCHS; do
+    if [ "$arch" = "arm64ec" ]; then
+        rm -f "$INSTALL_PREFIX/lib/windows/libclang_rt.builtins-aarch64.a" \
+              "$INSTALL_PREFIX/lib/windows/libclang_rt.builtins-arm64ec.a"
+        "$PREFIX/bin/llvm-lib" -machine:arm64ec "-out:$INSTALL_PREFIX/lib/windows/libclang_rt.builtins-aarch64.a" \
+                               build-aarch64/lib/windows/libclang_rt.builtins-aarch64.a \
+                               build-arm64ec/lib/windows/libclang_rt.builtins-arm64ec.a
+    fi
+done
+
 if [ "$INSTALL_PREFIX" != "$CLANG_RESOURCE_DIR" ]; then
     # symlink to system headers - skip copy
     rm -rf "$INSTALL_PREFIX/include"
diff --git a/build-libcxx.sh b/build-libcxx.sh
index f37cc9d..dcf4332 100755
--- a/build-libcxx.sh
+++ b/build-libcxx.sh
@@ -72,12 +72,6 @@ else
     esac
 fi
 
-for arch in $ARCHS; do
-    case $arch in
-    arm64ec) ARM64X_FLAGS="-marm64x" ;;
-    esac
-done
-
 for arch in $ARCHS; do
     [ -z "$CLEAN" ] || rm -rf build-$arch
     mkdir -p build-$arch
@@ -85,20 +79,12 @@ for arch in $ARCHS; do
     [ -n "$NO_RECONF" ] || rm -rf CMake*
 
     EXTRA_CFLAGS=""
-    EXTRA_LDFLAGS=""
     case $arch in
     i686|x86_64)
         # Force using the mingw stdio functions, for correct long double
         # printing.
         EXTRA_CFLAGS="-D__USE_MINGW_ANSI_STDIO=1"
         ;;
-    aarch64)
-        EXTRA_CFLAGS="$ARM64X_FLAGS"
-        EXTRA_LDFLAGS="$ARM64X_FLAGS"
-        ;;
-    arm64ec)
-        continue
-        ;;
     esac
 
     cmake \
@@ -133,8 +119,6 @@ for arch in $ARCHS; do
         -DLIBCXXABI_LIBDIR_SUFFIX="" \
         -DCMAKE_C_FLAGS_INIT="$CFGUARD_CFLAGS $EXTRA_CFLAGS" \
         -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS $EXTRA_CFLAGS" \
-        -DCMAKE_ASM_FLAGS_INIT="$EXTRA_CFLAGS" \
-        -DCMAKE_SHARED_LINKER_FLAGS="$EXTRA_LDFLAGS" \
         ..
 
     cmake --build . ${CORES:+-j${CORES}}
diff --git a/build-mingw-w64-libraries.sh b/build-mingw-w64-libraries.sh
index fd4a00f..6923558 100755
--- a/build-mingw-w64-libraries.sh
+++ b/build-mingw-w64-libraries.sh
@@ -55,36 +55,18 @@ if command -v gmake >/dev/null; then
     MAKE=gmake
 fi
 
-ARM64X_FLAGS=""
-for arch in $ARCHS; do
-    case $arch in
-    arm64ec) ARM64X_FLAGS="-marm64x" ;;
-    esac
-done
-
 cd mingw-w64/mingw-w64-libraries
 for lib in winpthreads winstorecompat; do
     cd $lib
-    FLAGS=""
     for arch in $ARCHS; do
-        case $arch in
-        aarch64)
-            FLAGS="$ARM64X_FLAGS"
-            ;;
-        arm64ec)
-            continue
-            ;;
-        esac
-
         [ -z "$CLEAN" ] || rm -rf build-$arch
         mkdir -p build-$arch
         cd build-$arch
         arch_prefix="$PREFIX/$arch-w64-mingw32"
         ../configure --host=$arch-w64-mingw32 --prefix="$arch_prefix" --libdir="$arch_prefix/lib" \
             --enable-silent-rules \
-            CFLAGS="$USE_CFLAGS $FLAGS" \
-            CXXFLAGS="$USE_CFLAGS $FLAGS" \
-            LDFLAGS="$FLAGS"
+            CFLAGS="$USE_CFLAGS" \
+            CXXFLAGS="$USE_CFLAGS"
         $MAKE -j$CORES
         $MAKE install
         cd ..
diff --git a/build-mingw-w64.sh b/build-mingw-w64.sh
index 6fb241e..e5f3916 100755
--- a/build-mingw-w64.sh
+++ b/build-mingw-w64.sh
@@ -105,10 +105,6 @@ $MAKE install
 cd ../..
 if [ -z "$SKIP_INCLUDE_TRIPLET_PREFIX" ]; then
     for arch in $ARCHS; do
-        case $arch in
-        arm64ec) continue ;;
-        esac
-
         mkdir -p "$PREFIX/$arch-w64-mingw32"
         if [ ! -e "$PREFIX/$arch-w64-mingw32/include" ]; then
             ln -sfn ../generic-w64-mingw32/include "$PREFIX/$arch-w64-mingw32/include"
@@ -116,24 +112,17 @@ if [ -z "$SKIP_INCLUDE_TRIPLET_PREFIX" ]; then
     done
 fi
 
-ARM64X_FLAGS=""
-for arch in $ARCHS; do
-    case $arch in
-    arm64ec) ARM64X_FLAGS="--enable-arm64x" ;;
-    esac
-done
-
 cd mingw-w64-crt
 for arch in $ARCHS; do
+    [ -z "$CLEAN" ] || rm -rf build-$arch
+    mkdir -p build-$arch
+    cd build-$arch
     case $arch in
     armv7)
         FLAGS="--disable-lib32 --disable-lib64 --enable-libarm32"
         ;;
-    aarch64)
-        FLAGS="--disable-lib32 --disable-lib64 --enable-libarm64 $ARM64X_FLAGS"
-        ;;
-    arm64ec)
-        continue
+    aarch64|arm64ec)
+        FLAGS="--disable-lib32 --disable-lib64 --enable-libarm64"
         ;;
     i686)
         FLAGS="--enable-lib32 --disable-lib64"
@@ -144,9 +133,6 @@ for arch in $ARCHS; do
     esac
     FLAGS="$FLAGS --with-default-msvcrt=$DEFAULT_MSVCRT"
     FLAGS="$FLAGS --enable-silent-rules"
-    [ -z "$CLEAN" ] || rm -rf build-$arch
-    mkdir -p build-$arch
-    cd build-$arch
     ../configure --host=$arch-w64-mingw32 --prefix="$PREFIX/$arch-w64-mingw32" $FLAGS $CFGUARD_FLAGS $CRT_CONFIG_FLAGS
     $MAKE -j$CORES
     $MAKE install
@@ -155,10 +141,6 @@ done
 cd ..
 
 for arch in $ARCHS; do
-    case $arch in
-    arm64ec) continue ;;
-    esac
-
     if [ ! -f $PREFIX/$arch-w64-mingw32/lib/libssp.a ]; then
         # Create empty dummy archives, to avoid failing when the compiler
         # driver adds "-lssp -lssh_nonshared" when linking.
diff --git a/build-openmp.sh b/build-openmp.sh
index 9c9d8fb..db69533 100755
--- a/build-openmp.sh
+++ b/build-openmp.sh
@@ -64,26 +64,12 @@ else
     esac
 fi
 
-ARM64X_FLAGS=""
-for arch in $ARCHS; do
-    case $arch in
-    arm64ec) ARM64X_FLAGS="-marm64x" ;;
-    esac
-done
-
 for arch in $ARCHS; do
     CMAKEFLAGS=""
-    FLAGS=""
     case $arch in
     x86_64)
         CMAKEFLAGS="$CMAKEFLAGS -DLIBOMP_ASMFLAGS=-m64"
         ;;
-    aarch64)
-        FLAGS="$ARM64X_FLAGS"
-        ;;
-    arm64ec)
-        continue
-        ;;
     esac
 
     [ -z "$CLEAN" ] || rm -rf build-openmp-$arch
@@ -104,9 +90,8 @@ for arch in $ARCHS; do
         -DCMAKE_RANLIB="$PREFIX/bin/llvm-ranlib" \
         -DLLVM_ENABLE_RUNTIMES="openmp" \
         -DLIBOMP_ENABLE_SHARED=TRUE \
-        -DCMAKE_C_FLAGS_INIT="$CFGUARD_CFLAGS $FLAGS" \
-        -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS $FLAGS" \
-        -DCMAKE_SHARED_LINKER_FLAGS="$FLAGS" \
+        -DCMAKE_C_FLAGS_INIT="$CFGUARD_CFLAGS" \
+        -DCMAKE_CXX_FLAGS_INIT="$CFGUARD_CFLAGS" \
         $CMAKEFLAGS \
         ..
     cmake --build . ${CORES:+-j${CORES}}
diff --git a/pgo-training.sh b/pgo-training.sh
index 709fdbb..0b279c5 100755
--- a/pgo-training.sh
+++ b/pgo-training.sh
@@ -54,20 +54,6 @@ if [ ! -d $SQLITE ]; then
     unzip sqlite-amalgamation-$SQLITE_VERSION.zip
 fi
 
-# pgo-training.make uses an explicit --sysroot pointing to the top of the llvm-mingw
-# installation (rather than the specific target prefix). This is currently not
-# supported by the Clang driver for arm64ec, which cannot use the arm64x prefix in
-# this configuration. Ideally, this should be fixed in Clang, but arm64ec provides
-# little additional profiling data compared to aarch64 anyway, so disable it for now.
-ORIG_ARCHS="$ARCHS"
-ARCHS=""
-for arch in $ORIG_ARCHS; do
-    case $arch in
-        arm64ec) continue ;;
-        *) ARCHS="$ARCHS $arch" ;;
-    esac
-done
-
 rm -rf "$LLVM_PROFILE_DATA_DIR"
 export ARCHS
 $MAKE -f pgo-training.make PREFIX=$PREFIX STAGE1=$STAGE1 SQLITE=$SQLITE clean
diff --git a/prepare-cross-toolchain-unix.sh b/prepare-cross-toolchain-unix.sh
index 1ef4969..7834e6d 100755
--- a/prepare-cross-toolchain-unix.sh
+++ b/prepare-cross-toolchain-unix.sh
@@ -51,10 +51,6 @@ rm -rf $DEST/lib/clang/*/lib/linux
 
 # Copy all arch-specific subdirectories plus the "generic" one, as is.
 for arch in generic $ARCHS; do
-    case $arch in
-    arm64ec) continue ;;
-    esac
-
     rm -rf $DEST/$arch-w64-mingw32
     cp -a $SRC/$arch-w64-mingw32 $DEST/$arch-w64-mingw32
 done
diff --git a/prepare-cross-toolchain.sh b/prepare-cross-toolchain.sh
index 724ce15..cfbcf6f 100755
--- a/prepare-cross-toolchain.sh
+++ b/prepare-cross-toolchain.sh
@@ -61,10 +61,6 @@ mkdir -p $DEST/include
 # individual architectures.
 cp -a $SRC/generic-w64-mingw32/include/. $DEST/include
 for arch in $ARCHS; do
-    case $arch in
-    arm64ec) continue ;;
-    esac
-
     mkdir -p $DEST/$arch-w64-mingw32
     for subdir in bin lib share; do
         cp -a $SRC/$arch-w64-mingw32/$subdir $DEST/$arch-w64-mingw32
diff --git a/run-tests.sh b/run-tests.sh
index c5ff0e8..882b997 100755
--- a/run-tests.sh
+++ b/run-tests.sh
@@ -210,7 +210,6 @@ for arch in $ARCHS; do
     unset HAVE_ASAN
     HAVE_UBSAN=1
     HAVE_OPENMP=1
-    prefix_arch="$arch"
     case $arch in
     i686)
         RUN="$RUN_I686"
@@ -243,7 +242,6 @@ for arch in $ARCHS; do
         RUN="$RUN_ARM64EC"
         COPY="$COPY_ARM64EC"
         NATIVE="$NATIVE_ARM64EC"
-        prefix_arch="aarch64"
         ;;
     esac
 
@@ -263,10 +261,10 @@ for arch in $ARCHS; do
     [ -z "$CLEAN" ] || rm -rf $TEST_DIR
     mkdir -p $TEST_DIR
     cd $TEST_DIR
-    $MAKE -f ../Makefile ARCH=$arch HAVE_UWP=$HAVE_UWP HAVE_CFGUARD=$HAVE_CFGUARD HAVE_ASAN=$HAVE_ASAN HAVE_UBSAN=$HAVE_UBSAN HAVE_OPENMP=$HAVE_OPENMP NATIVE=$NATIVE RUNTIMES_SRC=$PREFIX/$prefix_arch-w64-mingw32/bin clean
+    $MAKE -f ../Makefile ARCH=$arch HAVE_UWP=$HAVE_UWP HAVE_CFGUARD=$HAVE_CFGUARD HAVE_ASAN=$HAVE_ASAN HAVE_UBSAN=$HAVE_UBSAN HAVE_OPENMP=$HAVE_OPENMP NATIVE=$NATIVE RUNTIMES_SRC=$PREFIX/$arch-w64-mingw32/bin clean
     $MAKE -f ../Makefile ARCH=$arch HAVE_UWP=$HAVE_UWP HAVE_CFGUARD=$HAVE_CFGUARD HAVE_ASAN=$HAVE_ASAN HAVE_UBSAN=$HAVE_UBSAN HAVE_OPENMP=$HAVE_OPENMP NATIVE=$NATIVE $COPYARG $MAKEOPTS -j$CORES all
     if [ "$TARGET" != "all" ]; then
-        $MAKE -f ../Makefile ARCH=$arch HAVE_UWP=$HAVE_UWP HAVE_CFGUARD=$HAVE_CFGUARD HAVE_ASAN=$HAVE_ASAN HAVE_UBSAN=$HAVE_UBSAN HAVE_OPENMP=$HAVE_OPENMP NATIVE=$NATIVE RUNTIMES_SRC=$PREFIX/$prefix_arch-w64-mingw32/bin RUN="$RUN" $COPYARG $MAKEOPTS -j$CORES $TARGET
+        $MAKE -f ../Makefile ARCH=$arch HAVE_UWP=$HAVE_UWP HAVE_CFGUARD=$HAVE_CFGUARD HAVE_ASAN=$HAVE_ASAN HAVE_UBSAN=$HAVE_UBSAN HAVE_OPENMP=$HAVE_OPENMP NATIVE=$NATIVE RUNTIMES_SRC=$PREFIX/$arch-w64-mingw32/bin RUN="$RUN" $COPYARG $MAKEOPTS -j$CORES $TARGET
     fi
     cd ..
 done