[llvm] [NFC] Add explicit #include llvm-config.h where its macros are used. (PR #106621)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Ah, okay. I can see why it would be hard to static analysis tooling harder to figure that out given things can come from the compiler invocation on the CLI or from a header file.

It would be nice if there was a better way, but seems the best way to make do for now.

https://github.com/llvm/llvm-project/pull/106621