Minor fixes for CL compiler CTS test

With this series, if we also consume an updated SPIRV-LLVM-Translator with this patch, we can pass the test_compiler suite from the CL CTS.

The second commit is optional, it keeps us from asserting if we just compile a shader with an extern kernel without the translator patch, though linking will still fail, but is also a minor perf win, since it saves us from doing unnecessary work - we'll always want to link to remove linkage decorations.

The other patches fix up embedded header inclusion.

/cc @bbrezillon @daniels