CMake 2.8+ supports CMAKE_OSX_DEPLOYMENT_TARGET; don't do that stuff ourselves.

Do, however, do the "for a target of 10.4 or 10.5, build 32-bit only"
stuff, as that's specific to programs that capture traffic, such as
Wireshark (well, I guess we could just limit it to dumpcap, but...).

Change-Id: I5f4d4d57fd126e5c295dedae9ed13b263035a911
Reviewed-on: https://code.wireshark.org/review/3403
Reviewed-by: Guy Harris <guy@alum.mit.edu>