[clang] [LoongArch][clang] Add support for option `-msimd=` and macro `__loongarch_simd_width`. (PR #97984)

[Jake Egan via cfe-commits]

jakeegan wrote:

Hi, this test is failing on the AIX bot 
https://lab.llvm.org/buildbot/#/builders/64/builds/250/steps/6/logs/FAIL__Clang__loongarch-msimd_c

The reason is that -o is not a supported option with grep on AIX. Would you be able to adapt the test to avoid piping (so that the builtin grep is used, for example here: https://github.com/llvm/llvm-project/pull/83184/files) or use another command like sed?

https://github.com/llvm/llvm-project/pull/97984