[clang] Fix INF/NAN warning. (PR #80290)

[Aaron Ballman via cfe-commits]

================
@@ -2847,12 +2848,15 @@ class Preprocessor {
         !SourceMgr.isInMainFile(Identifier.getLocation()))
       emitRestrictExpansionWarning(Identifier);
 
-    if (Info->getName() == "INFINITY")
-      if (getLangOpts().NoHonorInfs)
-        emitRestrictInfNaNWarning(Identifier, 0);
-    if (Info->getName() == "NAN")
-      if (getLangOpts().NoHonorNaNs)
-        emitRestrictInfNaNWarning(Identifier, 1);
+    if (!IsIfnDef) {
+      bool UnsafeMath = getLangOpts().UnsafeFPMath;
+      if (Info->getName() == "INFINITY")
+        if (getLangOpts().NoHonorInfs)
+          emitRestrictInfNaNWarning(Identifier, 0, UnsafeMath);
+      if (Info->getName() == "NAN")
+        if (getLangOpts().NoHonorNaNs)
+          emitRestrictInfNaNWarning(Identifier, 1, UnsafeMath);
----------------
AaronBallman wrote:

```suggestion
      bool UnsafeMath = getLangOpts().UnsafeFPMath;
      if (Info->getName() == "INFINITY" && getLangOpts().NoHonorInfs)
        emitRestrictInfNaNWarning(Identifier, 0, UnsafeMath);
      if (Info->getName() == "NAN" && getLangOpts().NoHonorNaNs)
        emitRestrictInfNaNWarning(Identifier, 1, UnsafeMath);
```

https://github.com/llvm/llvm-project/pull/80290