[clang-tools-extra] Disable -Wsuggest-override for unittests/

[logan-5]

Summary

I added -Wsuggest-override to the LLVM build earlier today, and have been putting out small fires I caused since then. One sticky area here has been directories that have files that include googlemock and/or googletest headers, which unfortunately do not themselves use override, so I've had to add -Wno-suggest-override to the CMakeLists.txt's in those directories. This patch adds this same flag to CMakeLists.txt in clang-tools-extra/unittests. I just wanted to get the LGTM from one or more of you fine folks before I committed it.

[aaron.ballman]

LGTM, thanks!

clang-tools-extra/unittests/CMakeLists.txt

 add_custom_target(ExtraToolsUnitTests)
 set_target_properties(ExtraToolsUnitTests PROPERTIES FOLDER "Extra Tools Unit Tests")
 
 function(add_extra_unittest test_dirname)
   add_unittest(ExtraToolsUnitTests ${test_dirname} ${ARGN})
 endfunction()
 
+if (CXX_SUPPORTS_SUGGEST_OVERRIDE_FLAG)
+  add_definitions("-Wno-suggest-override")
+endif()
+
 add_subdirectory(clang-apply-replacements)
 add_subdirectory(clang-change-namespace)
 add_subdirectory(clang-doc)
 add_subdirectory(clang-include-fixer)
 add_subdirectory(clang-move)
 add_subdirectory(clang-query)
 add_subdirectory(clang-tidy)