Reland [NFC][CLANG] Fix nullptr dereference issue in SetValueDataBasedOnQualType()

This reverts commit 2b9ce77, which was
a temporary revert to get rebranch working.

Author: bnbarham

clang/lib/Interpreter/Interpreter.cpp

@@ -768,7 +768,7 @@ static void SetValueDataBasedOnQualType(Value &V, unsigned long long Data) {
   if (const auto *ET = QT->getAs<EnumType>())
     QT = ET->getDecl()->getIntegerType();
 
-  switch (QT->getAs<BuiltinType>()->getKind()) {
+  switch (QT->castAs<BuiltinType>()->getKind()) {
   default:
     llvm_unreachable("unknown type kind!");
 #define X(type, name)                                                          \