Keep into account if files were virtual.

In some cases we do not have files on disk. They are only available in the
FileManager as virtual files and the SourceManager overrides their content.

Author: vgvassilev

clang/lib/AST/ASTImporter.cpp

@@ -9906,7 +9906,7 @@ Expected<FileID> ASTImporter::Import(FileID FromID, bool IsBuiltin) {
       // FIXME: We want to re-use the existing MemoryBuffer!
       std::optional<llvm::MemoryBufferRef> FromBuf =
           Cache->getBufferOrNone(FromContext.getDiagnostics(),
-                                 FromSM.getFileManager(), SourceLocation{});
+                                 FromFileManager, SourceLocation{});
       if (!FromBuf)
         return llvm::make_error<ASTImportError>(ASTImportError::Unknown);
 

clang/lib/Frontend/VerifyDiagnosticConsumer.cpp

@@ -543,6 +543,11 @@ static bool ParseDirective(StringRef S, ExpectedData *ED, SourceManager &SM,
           OptionalFileEntryRef File =
               PP->LookupFile(Pos, Filename, false, nullptr, nullptr, nullptr,
                              nullptr, nullptr, nullptr, nullptr, nullptr);
+
+          // Check if the file was virtual
+          if (!File)
+            File = SM.getFileManager().getOptionalFileRef(Filename);
+
           if (!File) {
             Diags.Report(Pos.getLocWithOffset(PH.C - PH.Begin),
                          diag::err_verify_missing_file)