libmagic: Remove support for older FreeBSD where xlocale was not available.

The MINIMUM_SUPPORTED_OSREL is 1002501 (FreeBSD 10.3), and xlocale is
supported there.

While I'm there, explicitly use config.h generated with --disable-bzlib
--disable-xzlib instead of deleting them manually.

(cherry picked from commit 90266521018938b7b9f0003ba9a383b6920859e9)

file: Turns out we need xlocal.h protection

It turns out that we still need xlocal.h protection for when we're
cross building on Linux. Linux doesn't have this file, but os/x
does. Before, we'd assume we didn't have it, like old FreeBSD, when
cross compiling. After the latest update, all that code was removed so
cross compiling needs to be handled separaetly. Do so by defining
HAVE_XLOCALE_H only when we're not building on linux. This allows us
to build the mkmagic build tool needed to build file(1).

Sponsored by: Netflix
Reviewed by: jrtc27
Differential Revision: https://reviews.freebsd.org/D33741

(cherry picked from commit f3d7ace4b235422e5ccff0315f2965ac935241d8)