xcode-cross: Use the xcode clang toolchain directory as root director…

…y for the execution

The -no-canonical-prefixes makes clang not resolve the destination
of the symlink, when resolving the clang executable location, instead
just looking at the symlink that was invoked.

This makes clang use this directory as root for compiler-rt files
as well, which now matches the directory used for libc++ as well.

This makes the setup much more similar to what it is in the original
scenarios.

setup-toolchain.sh

@@ -84,6 +84,7 @@ export PATH=$CCTOOLS/bin:\$PATH
 if [ "\$TOOL" = "clang++" ] || [ "\$TOOL" = "c++" ] || [ "\$TOOL" = "g++" ]; then
 	ARGS+=(--driver-mode=g++)
 fi
+ARGS+=(-no-canonical-prefixes)
 EXE=\$(dirname \$(readlink -f \$0))/clang-exe
 \$EXE "\${ARGS[@]}"
 EOF
@@ -100,9 +101,15 @@ ln -s $CLANG/bin/dsymutil .
 ln -s $CLANG/bin/llvm-nm nm
 ln -s $CLANG/bin/clang clang-exe
 
-cd ../lib
-mkdir -p $CLANG/lib/arc
-ln -s $(pwd)/clang/*.*.*/lib/darwin $CLANG/lib/clang/*.*.*/lib
-for i in $(pwd)/arc/libarclite*.a; do
-	ln -s $i $CLANG/lib/arc
-done
+cd ../lib/clang
+# Rename the original bundled clang resource directory to "orig", to avoid
+# potential version number clashes.
+mv * orig
+# Fetch the version number of the resource directory of the clang we're
+# using.
+VER=$(cd $CLANG/lib/clang && ls)
+# Link in the clang resource directory from the external installation into
+# this directory.
+ln -s $CLANG/lib/clang/$VER .
+# Provide the original libraries in the external clang's resource directory.
+ln -s $(pwd)/orig/lib/darwin $VER/lib