Clang is being really peculiar.  Fix with:

-  inline hb_blob_t *sanitize (hb_blob_t *blob) { return c->sanitize<Type> (blob); }
+  inline hb_blob_t *sanitize (hb_blob_t *blob) { return c[0].template/*clang idiosyncrasy*/sanitize_blob<Type> (blob); }

Fixes #1105.

This new API returns cvXX and ssXX related NameId, things like
featUiLabelNameId, featUiTooltipTextNameId, sampleTextNameId, ... of cvXX
and UINameId of ssXX, in a unified way.

However HarfBuzz currently doesn't expose an API for retrieving the actual
information associated with NameId from the `name` table and that should be
done separately.

It had interesting stuffs like EXE parsing and
big-endian parsers but added in an attempt to find
a solution for #681 which later found not related.

We are not going to use them, at least in the foreseeable future

Previously the idea was to cache sanitize results externally (think,
in Fontconfig) and avoid resanitizing every time.  That's, not a good
idea.

Also, uncomment code again, just "if (0)" it out, so it doesn't get stale again.

Fixed the crasher in it.

This reverts commit 21fa170f.

Is crashing.  Oops.

Hopefully fixes bots.

Fixes https://github.com/harfbuzz/harfbuzz/issues/345

appveyor.yml: try updating msys2 to fix failing mingw-w64-x86_64 build

maybe it'll get a bit faster

so it won't attempt reinstalling packages which are already installed

https://github.com/harfbuzz/harfbuzz/pull/1093#issuecomment-405201903
https://ci.appveyor.com/project/harfbuzz/harfbuzz/build/job/ky7lao1ii1bi7ew4#L71

It uses constexpr...