[clang][Interp] Handle __extension__ for complex values

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -3839,6 +3839,9 @@ bool ByteCodeExprGen<Emitter>::VisitComplexUnaryOperator(
       return false;
     return DiscardResult ? this->emitPopPtr(E) : true;
 
+  case UO_Extension:
+    return this->delegate(SubExpr);
+
   default:
     return this->emitInvalid(E);
   }

clang/test/AST/Interp/complex.cpp

@@ -117,6 +117,9 @@ static_assert(__imag(Doubles[3]) == 0.0, "");
 
 static_assert(~(0.5 + 1.5j) == (0.5 + -1.5j), "");
 
+static_assert(__extension__ __imag(A) == 0, "");
+static_assert(__imag(__extension__ A) == 0, "");
+
 void func(void) {
   __complex__ int arr;
   _Complex int result;