[AST] Add a convenient getter from QualType to RecordDecl

Differential Revision: https://reviews.llvm.org/D49951

llvm-svn: 338187
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index cfd0b85..a738ecb 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -2064,8 +2064,7 @@
     if (record->isUnion()) {
       if (Field->getIdentifier())
         break;
-      if (const auto *FieldRD =
-              dyn_cast_or_null<RecordDecl>(Field->getType()->getAsTagDecl()))
+      if (const auto *FieldRD = Field->getType()->getAsRecordDecl())
         if (FieldRD->findFirstNamedDataMember())
           break;
     }