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

[Reid Kleckner via cfe-commits]

rnk wrote:

> Would it make sense to have a custom main for AllClangUnitTests and register all targets, just like clang driver does?

That sounds reasonable.

I toyed with the idea of putting the registration into a static initializer, but it raises the question of where you put it. Putting it into an existing test fixture file would work, but it's not nice. Registering targets in main like every other LLVM tool would be the obviously correct thing to do.

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