[clang] [Clang] Improve error for `-fsanitize=function/kcfi -mexecute-only` incompatibility (PR #118816)

[Csanád Hajdú via cfe-commits]

================
@@ -418,8 +418,14 @@ SanitizerArgs::SanitizerArgs(const ToolChain &TC,
                 Add & NotAllowedWithExecuteOnly & ~DiagnosedKinds) {
           if (DiagnoseErrors) {
             std::string Desc = describeSanitizeArg(Arg, KindsToDiagnose);
-            D.Diag(diag::err_drv_argument_not_allowed_with)
-                << Desc << Triple.str();
+            llvm::opt::Arg *A = Args.getLastArgNoClaim(
+                options::OPT_mexecute_only, options::OPT_mno_execute_only);
+            if (A && A->getOption().matches(options::OPT_mexecute_only))
+              D.Diag(diag::err_drv_argument_not_allowed_with)
+                  << Desc << A->getAsString(Args);
+            else
+              D.Diag(diag::err_drv_argument_not_allowed_with)
+                  << Desc << Triple.str();
----------------
Il-Capitano wrote:

Maybe `diag::err_drv_unsupported_opt_for_target` would be a better diagnostic in this case? That would produce
```
error: unsupported option '-fsanitize=function' for target '<triple>'
```

https://github.com/llvm/llvm-project/pull/118816