Work around clang miscompile.

Disable optimization on a function which returns a std::optional<bool>.

rdar://139105149

Author: nate-chandler

lib/AST/TypeCheckRequests.cpp

@@ -823,7 +823,9 @@ void RequiresOpaqueAccessorsRequest::cacheResult(bool value) const {
 // RequiresOpaqueModifyCoroutineRequest computation.
 //----------------------------------------------------------------------------//
 
-std::optional<bool>
+// NOTE: The [[clang::optnone]] annotation works around a miscompile in clang
+//       version 13.0.0 affecting at least Ubuntu 20.04, 22.04, and UBI 9.
+[[clang::optnone]] std::optional<bool>
 RequiresOpaqueModifyCoroutineRequest::getCachedResult() const {
   auto *storage = std::get<0>(getStorage());
   auto isUnderscored = std::get<1>(getStorage());