[clang] [clang] Inline static helper function in `Compilation.cpp` (PR #152875)

[via cfe-commits]

Sirraide wrote:

> @Sirraide, I do not really know who I should ping to review. Could you please help? Thanks!

I’ll merge it once CI is done w/ it (feel free to ping me again should I forget about it)

https://github.com/llvm/llvm-project/pull/152875