[clang] [clang][Sema] Shard out SemaTests into their own binary (PR #155548)

[Reid Kleckner via cfe-commits]

rnk wrote:

> I do my local build with -DBUILD_SHARED_LIBS=ON, so these are probably not the numbers you're looking for, but for the record, in my local build (which is a debug build), SemaTests is 6.7 MB, and clang is 2.1 MB. By comparison, AllClangUnitTests is 199.3 MB.

Yeah, the BUILD_SHARED_LIBS build completely negates the cost of additional gtest binaries, so doing what you're doing is sort of more natural.

I think in the spirit of not overthinking things, we can just land this, but we should add some comment about why this is a distinct unit test. I'll add a suggestion.

https://github.com/llvm/llvm-project/pull/155548