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.

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