Use `extern` where appropriate so that we can remove `-fcommon`
on macOS and others.  On macOS, `-fcommon` generates a number of
linker warnings.

I've tested building on macOS, Linux, FreeBSD, NetBSD, OpenBSD
and illumos.  I am not in a position to test on AIX or other
more esoteric platforms, however.

For fonts with subfiles that go beyond the xffff range, the font file size
calculation is incorrect, since lines beyond that range have additional
characters. This patch pads all of the ranges and subfont names with
leading zeros in order to keep them all lines the same length and fixes the
font file length calculation.

Drawing as white on black to produce a mask only works if
the white on black is the inversion of black on white.
Emoji that force use of specific colors don't respect that.
Draw black on white and invert to mask separately.

Co-authored-by: dzklaim <smmoth.rp@gmail.com>

Have to adjust algorithms to deal with
much larger number of subfont files as well.

We were using osx- and cocoa- but it's not even OS X anymore.

Some truetype fonts have good manual hinting.
Ignoring hinting makes the font render badly on low resolution screens.
This commit only disables the freetype autohinter, and allows hinting.

Remote whitespace at the ends of lines.
Remove blank lines from the ends of files.
Change modes on source files so that they
are not executable.

Signed-off-by: Dan Cross <cross@gajendra.net>