[coroutines] Add overloaded unary 'operator co_await'.

llvm-svn: 250991
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index c4e1b26..705e6f5 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -6385,6 +6385,7 @@
   case OO_Call:
   case OO_Subscript:
   case OO_Conditional:
+  case OO_Coawait:
   case NUM_OVERLOADED_OPERATORS:
     llvm_unreachable("Unexpected reduction identifier");
   case OO_None: