[clang] [flang] [Clang][Driver][fveclib] Fix target parsing for -fveclib=AMDLIBM option (PR #140544)

[Paul Walker via cfe-commits]

================
@@ -5844,7 +5844,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
           Triple.getArch() != llvm::Triple::x86_64)
         D.Diag(diag::err_drv_unsupported_opt_for_target)
             << Name << Triple.getArchName();
-    } else if (Name == "libmvec") {
+    } else if (Name == "libmvec" || Name == "AMDLIBM") {
----------------
paulwalker-arm wrote:

There's equivalent code in `Flang.cpp` that's also worth updating.

https://github.com/llvm/llvm-project/pull/140544