Some macs appear to need "-framework CoreFoundation" added to the linking
step, others (which appear to have the exact same OS and tools installed),
don't. But as it doesn't appeart to hurt, I unconditionally add this.
Switched to using pkgconfig to find libdivecomputer on the Mac.
Tried to clean up the Makefile a bit
Signed-off-by: Dirk Hohndel <dirk@hohndel.org> Acked-by: Henrik Brautaset Aronsen <subsurface@henrik.synth.no>