Update the OS X Puzzles makefile so that it builds on Leopard and

generates PPC/Intel dual-architecture binaries.

This turns out not to be too painful: you compile and link your
programs using `gcc -arch ppc' or `gcc -arch i386', then you use a
command of the form `lipo -create ppc-binary i386-binary -output
binary' to construct a universal binary. It works equally well on
command-line standalone executable files and the executables within
application directories. Also added the -mmacosx-version-min option,
since otherwise the OS X build tools appear to default to building
binaries which will crash (without anything resembling a
comprehensible error message) on any earlier release.

The handling of version.o in this checkin is somewhat grotty. I'd
prefer a method more cleverly intertwingled with mkfiles.pl so I
didn't have to maintain the OS X architecture list in both
mkfiles.pl and Recipe. (Not that I anticipate Apple switching
architectures again in the immediate future, but it's the principle
of the thing.)

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@7916 cda61777-01e9-0310-a592-d414129be87e