Revert "Add ARM64X support"

This reverts commit 64effa9a71.

It turns out that the LLD handling of the TLS data structures
("_tls_used" and "_tls_index") needs more work, causing the
arm64ec side of arm64x binaries to not get them hooked up properly.

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"