[libcxx-commits] [libcxx] [libcxx] Define `_LIBCPP_HAS_C8RTOMB_MBRTOC8` to true if compiling with clang (PR #152724)

[Victor Campos via libcxx-commits]

vhscampos wrote:

@philnik777 @ldionne
The premerge CI jobs found some outstanding issues. The PR still has some issues to iron out. Here's the summary:

- armv7, armv8, aarch64: Linux, Arm targets, clang, glibc < 2.36. Macro is true, so `char8`functions are declared in libcxx despite not available in glibc. `error: reference to unresolved using declaration`.
- stage1 (generic-gcc, gcc-16, g++-15):  Linux, x86_64, gcc, glibc < 2.36. Macro is false, so `char8`functions are NOT declared in libcxx. `error: ‘mbrtoc8’ is not a member of ‘std’`.
- stage1 (generic-cxx26, clang-22, clang++-22): Linux, x86_64, clang, glibc < 2.36. Macro is true, so `char8`functions are declared in libcxx despite not available in glibc. `error: reference to unresolved using declaration`.
- stage 1 (generic-modules, clang-22, clang++-22): Linux, x86_64, clang, glibc < 2.36. Macro is true, so `char8`functions are declared in libcxx despite not available in glibc. `error: reference to unresolved using declaration`.

I don't know how to specify xfails to capture the conditions of these failures, or if it's even possible. If I xfail it on Linux across the board, I think it will unexpectedly pass on downstream runners that have a newer glibc.

I'm lost here. Do you have any recommendations to make progress on this?

https://github.com/llvm/llvm-project/pull/152724