[libcxx-commits] [libcxx] [libc++][test] Improves substitution naming (PR #80471)

[Louis Dionne via libcxx-commits]

ldionne wrote:

CC @llvm/libcxx-vendors , this may require tiny changes to your downstream setup if you have custom Lit config files.

https://github.com/llvm/llvm-project/pull/80471