[CMake] support for OSX universal binaries added to CMake CVS

[Bill Hoffman]

I have just checked in support for universal binaries in CVS CMake.
If you run cmake on a mac with a version of the compiler that supports
universal binaries, you will get two new cache entires:

CMAKE_OSX_ARCHITECTURES  - defaults to ppc or i386 (uses uname)
CMAKE_OSX_SYSROOT - defaults to /Developer/SDKs/MacOSX10.4.u.sdk if it is 
on the machine.

If you change CMAKE_OSX_ARCHITECTURES  to have ppc;i386 it will build a
universal binary.  This works for both Xcode and makefiles.

-Bill