[clang] [HIP] change default offload archs (PR #139281)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

The main obstacle of letting clang emit error when `--offload-arch` is not specified is HIP apps using hipcc as CMAKE_CXX_COMPILER. hipcc adds -xhip by default for .cpp programs. This is a known and long existing issue.

Another option is to have multiple `--offload-arch` options by default, which covers gfx9 generic, gfx10 generic, gfx11 generic, and gfx12 generic. This should make the program work for most of GPU's.

https://github.com/llvm/llvm-project/pull/139281