[clang] Fix Issue where libclang Does Not Include Standard Compiler Specific Headers (PR #153746)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

If we're going to explicitly add a flag for the resource dir, we should use the flag `-resource-dir`, not try to emulate it with -I.  There are other relevant bits in the resource directory, like cfi_ignorelist.txt.

We have code in libclang which is supposed to handle this; clang_parseTranslationUnit_Impl calls getClangResourcesPath() to try to compute the path to the resource dir.  I'm not sure if we're computing the right path, though, or if we actually pass it down to the driver correctly.

https://github.com/llvm/llvm-project/pull/153746