[HarfBuzz] harfbuzz: Changes to 'check-symbols'

[Behdad Esfahbod]

New branch 'check-symbols' available with the following commits:
commit 009541247c608ad31e532efdf224fd09244474a5
Author: Behdad Esfahbod <behdad at behdad.org>
Date:   Wed Feb 21 14:36:45 2018 -0800

    Clean up check-defs and check-symbols
    
    I probably broken Mac test. I'm going to merge the two tests and bot-happy
    it after.
    
    Also, call c++filt on their results.