[clang] feat: included support for is_constant builtin (PR #166832)

[Henrich Lauko via cfe-commits]

================
@@ -199,6 +199,43 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
     return RValue::get(
         builder.createBitcast(allocaAddr, builder.getVoidPtrTy()));
   }
+  
+  case Builtin::BI__builtin_constant_p: { 
+    mlir::Location loc = getLoc(e->getSourceRange());
+    mlir::Type ResultType = convertType(e->getType());
+
+    const Expr *Arg = e->getArg(0);
+    QualType ArgType = Arg->getType();
----------------
xlauko wrote:

```suggestion
    const Expr *arg = e->getArg(0);
    QualType argType = arg->getType();
```

https://github.com/llvm/llvm-project/pull/166832