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

[Joseph Huber via cfe-commits]

================
@@ -1115,14 +1117,13 @@ def fno_convergent_functions : Flag<["-"], "fno-convergent-functions">,
 
 // Common offloading options
 let Group = offload_Group in {
-def offload_arch_EQ : Joined<["--"], "offload-arch=">, Flags<[NoXarchOption]>,
----------------
jhuber6 wrote:

I definitely agree now that it works on all the targets. I was actually shocked what I saw that `-Xarch_` didn't even have help text. Would that be a follow-up?

Also, if we *really* wanted the above to work, we could do a special-case handling that only accepts the pair of `-Xarch_<arch> --offload-arch=<arch>` but I think that would be awful.

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