[cxx-interop] Allow using non-resilient C++ symbols in resilient overlays

If a Swift module built with library evolution enabled is an overlay of a C++ module, allow referring to the non-resilient C++ symbols from the Swift code.

Overlays are usually built and shipped along with the C/C++ modules, so library evolution is less of a concern there. A developer providing a Swift overlay for a C++ library would expect to be able to refer to the symbols from the C++ library within the overlay.

Author: egorzhdan

lib/Sema/TypeCheckAccess.cpp

@@ -2002,6 +2002,10 @@ swift::getDisallowedOriginKind(const Decl *decl,
   if (SF->getASTContext().LangOpts.EnableCXXInterop && where.getDeclContext() &&
       where.getDeclContext()->getAsDecl() &&
       where.getDeclContext()->getAsDecl()->getModuleContext()->isResilient() &&
+      !where.getDeclContext()
+           ->getAsDecl()
+           ->getModuleContext()
+           ->getUnderlyingModuleIfOverlay() &&
       decl->hasClangNode() && !decl->getModuleContext()->isSwiftShimsModule() &&
       isFragileClangNode(decl->getClangNode()) &&
       !SF->getASTContext().LangOpts.hasFeature(

stdlib/public/Cxx/std/CMakeLists.txt

@@ -55,7 +55,6 @@ add_swift_target_library(swiftCxxStdlib STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_O
     SWIFT_COMPILE_FLAGS ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS} ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
     -cxx-interoperability-mode=default
     -Xfrontend -module-interface-preserve-types-as-written
-    -enable-experimental-feature AssumeResilientCxxTypes
 
     # The varying modularization of the C++ standard library on different
     # platforms makes it difficult to enable MemberImportVisibility for this