[clang] [Clang] __has_builtin should return false for aux triple builtins (PR #121839)

[Nick Sarnie via cfe-commits]

sarnex wrote:

`.CodeGenHipStdPar/unsupported-builtins.cpp` is pretty interesting actually, it looks like it tests for some behavior in CodeGen that seems like it's trying to fix the exact same problem

https://github.com/llvm/llvm-project/pull/121839