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 the SDL AmigaOS audio subsystem

noinst_LTLIBRARIES = libaudio_arch.la

ARCH_SRCS = SDL_ahiaudio.c SDL_ahiaudio.h

libaudio_arch_la_SOURCES = $(ARCH_SRCS)