Update autoconf file to build against libapparmor

Update autoconf file to build against libapparmor

AppArmor support can be configured at build time with --enable-apparmor
and --disable-apparmor. By default, the build time decision is
automatically decided by checking if a sufficient libapparmor is
available.

A minimum required libapparmor is version 2.8.95.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=75113
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
[smcv: avoid potential non-portability from "test EXPR -a EXPR"]
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>