message: [SwiftASTContext] Pass OverlayFileSystem to source manager
diff: @@ -2645,9 +2645,12 @@ swift::CompilerInvocation &SwiftASTContext::GetCompilerInvocation() {
  }
  swift::SourceManager &SwiftASTContext::GetSourceManager() {
  - if (!m_source_manager_up)
  - m_source_manager_up = llvm::make_unique<swift::SourceManager>(
  - FileSystem::Instance().GetVirtualFileSystem());
  + if (!m_source_manager_up) {
  + auto OverlayFS = llvm::IntrusiveRefCntPtr<llvm::vfs::OverlayFileSystem>(
  + new llvm::vfs::OverlayFileSystem(llvm::vfs::getRealFileSystem()));
  + OverlayFS->pushOverlay(FileSystem::Instance().GetVirtualFileSystem());
  + m_source_manager_up = llvm::make_unique<swift::SourceManager>(OverlayFS);
  + }
  return *m_source_manager_up;
  }
  