Skip Unions when selecting from randomization

There's no harmful effect if we DO randomize a union, however,
since all of a union's data members have their offsets set to 0
there's no advantage for our code to run anyway. This way we can
spare some CPU cycles in the event that someone adds the randomize
attribute to their union.

Author: connorkuehl

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -2990,7 +2990,7 @@ ASTContext::getASTRecordLayout(const RecordDecl *D) const {
 
   bool ShouldBeRandomized = D->getAttr<RandomizeLayoutAttr>() != nullptr;
 
-  if (ShouldBeRandomized) {
+  if (ShouldBeRandomized && !D->isUnion()) {
     Randstruct randstruct;
     randstruct.reorganizeFields(*this,D);
   }