automake: loader: don't create an empty dri3 helper

automake: loader: don't create an empty dri3 helper

Seems that creating an empty one does not fair too well with MacOSX's
ar. Considering that all the users of the helper include it only when
needed, let's reshuffle the makefile.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92985
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Tested-by: Vinson Lee <vlee@freedesktop.org>
Tested-by: Kai Wasserbäch <kai@dev.carbon-project.org>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>