prepare-cross-toolchain-unix: Remove the linux/macOS runtimes

This matches what is done in build-all.sh for the PGO step; this
removes rather large (~50 MB) libraries that mostly are needed
for compiling for the host unix platforms. (On Linux it's needed
if building with profiling, on macOS it's needed for the builtin
functions for platform version availability too.)

Author: mstorsjo

prepare-cross-toolchain-unix.sh

@@ -44,6 +44,11 @@ CLANG_VERSION=$(basename "$CLANG_RESOURCE_DIR")
 rm -rf $DEST/lib/clang/$CLANG_VERSION
 cp -a $CLANG_RESOURCE_DIR $DEST/lib/clang/$CLANG_VERSION
 
+# Remove the native Linux/macOS runtimes which aren't needed in
+# the final distribution.
+rm -rf $DEST/lib/clang/*/lib/darwin
+rm -rf $DEST/lib/clang/*/lib/linux
+
 # Copy all arch-specific subdirectories plus the "generic" one, as is.
 for arch in generic $ARCHS; do
     rm -rf $DEST/$arch-w64-mingw32