Add clang tool switch to traffic annotation auditor.

A switch is added to clang tool calls from traffic annotation auditor,
to ignore constant comparisons.
Some tests compare constants to prevent future regressions, but clang
sees these as unnecessary comparisons and issues error.

Bug: 690323
Change-Id: Iaa194641f2d6a8cd66ae61f514703bccc28967da
Reviewed-on: https://chromium-review.googlesource.com/958518
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543045}

tools/traffic_annotation/auditor/traffic_annotation_auditor.cc

@@ -161,7 +161,8 @@ bool TrafficAnnotationAuditor::RunClangTool(
       "--tool-path=%s "
       "--tool-arg=--extra-arg=-resource-dir=%s "
       "--tool-arg=--extra-arg=-Wno-comment "
-      "--tool-arg=--extra-arg=-Wno-tautological-unsigned-enum-zero-compare ",
+      "--tool-arg=--extra-arg=-Wno-tautological-unsigned-enum-zero-compare "
+      "--tool-arg=--extra-arg=-Wno-tautological-constant-compare ",
       build_path_.MaybeAsASCII().c_str(),
       base::MakeAbsoluteFilePath(clang_tool_path_).MaybeAsASCII().c_str(),
       base::MakeAbsoluteFilePath(GetClangLibraryPath()).MaybeAsASCII().c_str());