Chrome Version       : 68.0.3414.0
URLs (if applicable) :
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari:
    Firefox:
       Edge:

What steps will reproduce the problem?
(1)sudo apt-get install ccache
(2)added cc_wrapper="ccache" to gn args out/Default
(3)ran ninja -C out/Default chrome
(4)got many of the following errors about unused isystem flags:
clang++: error: argument unused during compilation: '-isystem ../../buildtools/third_party/libc++/trunk/include' [-Werror,-Wunused-command-line-argument]

What is the expected result?
ninja build completes successfully

What happens instead?
stops on errors

Please provide any additional information below. Attach a screenshot if
possible.
Building on ubuntu.