Seperate glX from HAVE_OPENGL, for platforms that have both an X server and a more official way to do OpenGL, explicitly check for glX on Mac OS X, and use SDL_LoadObject for platforms that have glX but don't have dlopen().

## Makefile.am for SDL using the AIX UMS sound driver

noinst_LTLIBRARIES = libaudio_ums.la
libaudio_ums_la_SOURCES = $(SRCS)

# The SDL audio driver sources
SRCS =	SDL_umsaudio.c	\
	SDL_umsaudio.h