Some of our bots / compilers don't like it. Wasn't caught by bots because this
is only in debug code.

https://github.com/harfbuzz/harfbuzz/pull/809/commits/825ad378e0f0e6e6bb690894a0d5d25f198be21b

Fixes Chromium Android builds, compare
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/491787

Fixes #805

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=6022

Context needs to be called 'c'. The TRACE_* rely on that.

Previously adjusted logic could fail if nothing around was ligated,
and something moved.  This should take care of that.

CC https://github.com/harfbuzz/harfbuzz/issues/740

Add a continuous builder using fswatch

I hope I am in a correct direction at least

Optimize set through optimized bit operations

Should fix Win64 bot.

Fixes #791.

Should bring bag djgpp bot.

[subset] Use gids_to_retain_sorted to produce old gid -> new gid mapping since it now has the more complete set.