Spun off from:
https://chromium-review.googlesource.com/c/chromium/src/+/1421920/8#message-6deb3b1243af6bb2bf3fc4363073cc7a7098e5d2


Takuto Ikuta writes:

> Hi, this CL made build output noisy in chromium build. e.g. many warning compile output
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8923958932300105056/+/steps/compile__with_patch_/0/stdout

> Can I ask you to suppress the warning?
> I don't think it is good to enable warning in header file. It is not common and hard to find the reason of warning.
https://github.com/harfbuzz/harfbuzz/blob/89bcfb204c736f5962d377896af2c1350f179882/src/hb.hh