clang: Fix nativesdk build after recipe splits

clang: Fix nativesdk build after recipe splits

Splitting llvm, tblgen into their own recipes means we
have to ensure nativesdk clang build can find these tools
in native sysroot, which is would previously build and use
on its own.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>