[clang][Interp] Fix ignoring String- and CharacterLiterals

clang/lib/AST/Interp/ByteCodeExprGen.cpp

bool ByteCodeExprGen<Emitter>::VisitAbstractConditionalOperator(
     const AbstractConditionalOperator *E) {
   return this->visitConditional(E, [this](const Expr *E) {
     return DiscardResult ? this->discard(E) : this->visit(E);
   });
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitStringLiteral(const StringLiteral *E) {
+  if (DiscardResult)
+    return true;
   unsigned StringIndex = P.createGlobalString(E);
   return this->emitGetPtrGlobal(StringIndex, E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCharacterLiteral(
     const CharacterLiteral *E) {
+  if (DiscardResult)
+    return true;
   return this->emitConst(E->getValue(), E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitFloatCompoundAssignOperator(
     const CompoundAssignOperator *E) {
   assert(E->getType()->isFloatingType());
 

clang/test/AST/Interp/literals.cpp

constexpr int ignoredExprs() {
 
     1 ? 0 : 1;
     __is_trivial(int);
 
     (int){1};
     (int[]){1,2,3};
     int arr[] = {1,2,3};
     arr[0];
+    "a";
+    'b';
 
     return 0;
   }
 
   constexpr int oh_my(int x) {
     (int){ x++ };
     return x;
   }