fontconfig: update 2.15.0 -> 2.17.1

fontconfig: update 2.15.0 -> 2.17.1

Tarballs have relocated to gitlab.

Convert to meson.

License-update: trim the code, keep only the license
(there used to be a second copyright notice from a different author but
with mostly same MIT-ish content)

Add a backport to fix musl builds.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>