[clang][Interp] Fix ignoring conditional operators

[tbaeder]

Ping

[shafik]

LGTM

clang/lib/AST/Interp/ByteCodeExprGen.cpp

 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitOpaqueValueExpr(const OpaqueValueExpr *E) {
   return this->visit(E->getSourceExpr());
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitAbstractConditionalOperator(
     const AbstractConditionalOperator *E) {
-  return this->visitConditional(
-      E, [this](const Expr *E) { return this->visit(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) {
   unsigned StringIndex = P.createGlobalString(E);
   return this->emitGetPtrGlobal(StringIndex, E);
 }
 

clang/test/AST/Interp/literals.cpp

constexpr int ignoredExprs() {
   a; // expected-warning {{unused}} \
      // ref-warning {{unused}}
   (void)a;
   (a); // expected-warning {{unused}} \
        // ref-warning {{unused}}
 
   (void)5, (void)6;
 
+  1 ? 0 : 1; // expected-warning {{unused}} \
+             // ref-warning {{unused}}
+
   return 0;
 }
 
 /// Ignored comma expressions still have their
 /// expressions evaluated.
 constexpr int Comma(int start) {
     int i = start;