[clang-tidy] Count errors in ClangTidyDiagnosticConsumer

This re-applies r222363 reverted in r222390 after compilation errors in our
out-of-tree clang-tidy tests were fixed.

llvm-svn: 222427

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp

@@ -277,6 +277,9 @@ void ClangTidyDiagnosticConsumer::finalizeLastError() {
 
 void ClangTidyDiagnosticConsumer::HandleDiagnostic(
     DiagnosticsEngine::Level DiagLevel, const Diagnostic &Info) {
+  // Count warnings/errors.
+  DiagnosticConsumer::HandleDiagnostic(DiagLevel, Info);
+
   if (DiagLevel == DiagnosticsEngine::Note) {
     assert(!Errors.empty() &&
            "A diagnostic note can only be appended to a message.");

clang-tools-extra/test/clang-tidy/clang-tidy-diff.cpp

@@ -6,7 +6,7 @@ struct A {
   virtual void f() {}
   virtual void g() {}
 };
-// CHECK-NOT: warning
+// CHECK-NOT: warning:
 struct B : public A {
   void placeholder_for_f() {}
 // CHECK-SANITY: [[@LINE-1]]:8: warning: Annotate this