Previously was failing to match fonts that didn't support CHARSET_ANSI.

There still remains a problem with the Uniscribe backend, in that if a
font with the same family name is installed, and is newer, the native
one is preferred over the font we provide.  Fixing it requires rewriting
the name table with a unique family name...

Introduced in 99c26957.
Broken mark-mark and mark-ligature stuff.

Oops.  hb_tag_t and OPENTYPE_TAG have different endianness.  Perhaps
something to add API for in hb-uniscribe.h

Matches OT backend now.

Detected by clang and lots of cmdline options.

As reported by bashi.  Not tested.