[libclc] [libclc] Append file_specific_compile_options after ARG_COMPILE_FLAGS (PR #139871)

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

Sure, no problem. You can probably request [commit access](https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access) by now, though.

https://github.com/llvm/llvm-project/pull/139871