[clang][bytecode] Fix __extension__ handling for vector operators (llvm#118482)

Don't reject them, but delegate to the subexpression.

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -5914,6 +5914,9 @@ bool Compiler<Emitter>::VisitVectorUnaryOperator(const UnaryOperator *E) {
     return this->discard(SubExpr);
 
   auto UnaryOp = E->getOpcode();
+  if (UnaryOp == UO_Extension)
+    return this->delegate(SubExpr);
+
   if (UnaryOp != UO_Plus && UnaryOp != UO_Minus && UnaryOp != UO_LNot &&
       UnaryOp != UO_Not && UnaryOp != UO_AddrOf)
     return this->emitInvalid(E);

clang/test/AST/ByteCode/vectors.cpp

@@ -37,6 +37,7 @@ static_assert(arr4[1][0] == 0, "");
 static_assert(arr4[1][0] == 0, "");
 static_assert(arr4[1][0] == 0, "");
 
+constexpr VI4 B = __extension__(A);
 
 /// From constant-expression-cxx11.cpp
 namespace Vector {