[clang] [clang] Make -fveclib={ArmPL, SLEEF} imply -fno-math-errno (PR #112580)

[Paul Walker via cfe-commits]

================
@@ -2960,6 +2969,12 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
   }
 
   for (const Arg *A : Args) {
+    auto CheckMathErrnoForVecLib =
+        llvm::make_scope_exit([&, MathErrnoBeforeArg = MathErrno] {
+          if (NoMathErrnoWasImpliedByVecLib && !MathErrnoBeforeArg && MathErrno)
+            ArgThatEnabledMathErrnoAfterVecLib = A;
+        });
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paulwalker-arm wrote:

I don't think we need such complexity.  Given all the variables exist you can just clear `ArgThatEnabledMathErrnoAfterVecLib` within the `OPT_fveclib` case block and then have

```
if (NoMathErrnoWasImpliedByVecLib && !ArgThatEnabledMathErrnoAfterVecLib && MathErrno)
  ArgThatEnabledMathErrnoAfterVecLib = A
```
just before we claim `A` after the switch block.
  

https://github.com/llvm/llvm-project/pull/112580