[clang] [Clang] Make `-Xarch_` handling generic for all toolchains (PR #125421)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

Here's something fun, `-O0` and `-O3` are accepted by `-Xarch` but `-O1` and `-O2` are rejected.

https://github.com/llvm/llvm-project/pull/125421