[llvm-branch-commits] [libcxx] [llvm] release/20.x: [libcxx] Provide locale conversions to tests through lit substitution (#105651) (PR #139468)

[Martin Storsjö via llvm-branch-commits]

mstorsjo wrote:

This is a manual backport attempt of the same as #136449, with some more fixes included. This should unbreak the libcxx CI on macOS on the release branch, which seems to be broken as is.

https://github.com/llvm/llvm-project/pull/139468