llvm-project

26a766ae - Make sure all matrix options are run in libc premerge testing (#146162)

Make sure all matrix options are run in libc premerge testing (#146162) https://github.com/llvm/llvm-project/pull/126315 changes the premerge testing to build in Debug, Release, and MinSizeRel configs, as opposed to only MinSizeRel, but for some reason the matrix is not returning all options now. Fix so that it actually builds the intended configs. Per discussion in [146161](https://github.com/llvm/llvm-project/issues/146161), only test all three configs on Linux x86_64. Other OS's and configurations will build in Debug mode only. Also fix a cmake variable and remove outdated comments. Bug: https://github.com/llvm/llvm-project/issues/146161