automake: create compat symlinks only for linux systems

automake: create compat symlinks only for linux systems

The primary users of these are linux developers, although
it can be extended for *BSD and others if needed.

Fixes make install for Cygwin and OpenBSD at least.

v2:
 - Wrap vdpau targets as well.
v3:
 - Fold HAVE_COMPAT_SYMLINKS conditional within install*links.mk

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=63269
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Jon TURNEY <jon.turney@dronecode.org.uk> (v1)
Reviewed-by: Christian König <christian.koenig@amd.com>