[clang] Returning library functions as integer instead of bool (PR #166446)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

Looks good, but this PR does need a good description before it can be merged.

Among other things, it should mention that
— you removed a lot of `# type: ignore` annotations
— return value of `clang_File_isEqual` has been already passed to `bool` constructor
— return value of `clang_isFileMultipleIncludeGuarded` is not passed to a bool constructor, because the function is never used.

https://github.com/llvm/llvm-project/pull/166446