The OS X backend Makefile.am was missing a line concatenation, and
so the -xobjective-c directive was always ignored.
Instead of dumping everything into INCLUDES and LDADD we should follow
what the rest of the backends do, and use per-target CFLAGS and LDADD,
and reserve the INCLUDES to -D and -I directives.
Thanks to: Christian Hergert <chris@dronelabs.com>
dfc32b60c4