[clang] [clang] Merge gtest binaries into AllClangUnitTests (PR #134196)

[Reid Kleckner via cfe-commits]

rnk wrote:

> `BasicTests` and `FormatTests` had fairly few deps (they didn't need Sema etc) and compiled much fewer files than they presumably now do. Does it make sense to keep those as distinct binaries?

FormatTests has many clang dependencies, but after rebuilding, it looks like it's still quite small, so I sent a PR with my file size data:
https://github.com/llvm/llvm-project/pull/138021

You can see that the Interpreter tests are a much bigger target for optimization.

https://github.com/llvm/llvm-project/pull/134196