prepare-cross-toolchain: Include other compiler-rt files too (headers and auxillary files)

prepare-cross-toolchain.sh

@@ -37,8 +37,21 @@ for i in libc++ libunwind; do
     fi
 done
 
-# Copy the clang bundled runtime libraries (compiler-rt)
+# Copy the clang resource files (include, lib, share). The clang cross
-cp -a $CLANG_RESOURCE_DIR/lib $DEST/lib/clang/$CLANG_VERSION
+# build installs the main headers, but since we didn't build the runtimes
+# (compiler-rt), we're lacking the files that are installed by them. The
+# compiler-rt build primarily installs some libs, but also a few files under
+# share, and headers for some of the runtime libraries.
+#
+# Instead of trying to merge these files on top of the headers installed
+# by the clang cross build, just wipe the existing files and copy the whole
+# resource directory from the complete toolchain. As long as it's a matching
+# version of clang, the headers that were installed by it should be identical.
+#
+# Alternatively, we could copy the lib and share subdirectories, and
+# copy the individual include subdirectories that are missing.
+rm -rf $DEST/lib/clang/$CLANG_VERSION
+cp -a $CLANG_RESOURCE_DIR $DEST/lib/clang/$CLANG_VERSION
 
 rm -rf $DEST/include
 # Copy over headers and arch specific files, converting a unix style