[llvm] [lit] Support GoogleTest test discovery through prefixes, too (PR #137423)

[Reid Kleckner via llvm-commits]

rnk wrote:

Separately, if you're interested in tuning up the way we run gtests, feel free to take a look at https://github.com/llvm/llvm-project/pull/134196

https://github.com/llvm/llvm-project/pull/137423