This allows all SDL code to take advantage of the atomic intrinsics on Windows, but doesn't cause applications just including SDL.h to pull in windows.h
Changed the CAS return value to bool, so it's efficient with OSAtomicCompareAndSwap32Barrier()
Added an atomic test adapted from code by Michael Davidsaver
The linux code appears to be complete and *should* be the base of all Unix and GCC based versions. The macosx and win32 versions
are currently just copies of the dummy code. I will begin working on the windows version as soon as this check in is done. I
need someone to work on the Mac OS X version.
I'm afraid that this check in will break QNX (Sorry!)
/test/testatomic.c performs absolutely basic tests to show that the function work as expected. Need a second test to do more detailed tests.
/include/SDL_atomic.h provides declarations for all included functions.
/src/atomic/linux/SDL_atomic.c provided all the functions. On a generic built the 64 bit functions work, but they are emulated. On a build for -march=pentium and above the 64 bit functions use native instructions
/src/atomic/dummy/SDL_atomic.c emulates all the operations using SDL_mutex.h.
/src/atomic/win32/SDL_atomic.c is a copy of dummy
/src/atomic/macosx/SDL_atomic.s is a copy of dummy
These versions of SDL_atomic.c provide a frame work for building the library with a mixture of native and emulated functions. This allows the whole library to be provided on all platforms. (I hope.)
I hope this fits with the SDL philosophy of either providing a common subset or emulating when the platform is missing a feature.
I have not added dummy, macosx, or win32 to the build. They are there as place holders for future work.
I have modified congifure.in to compile sources in /src/atomic/linux. (The SDL configure.in file is an amazing piece of work and I hope I didn't mess it up. :-)
It also update configure.in to compile the linux version of the library. The three versions are all dummies
implementations that do nothing. They are being checked in as place holders. Mostly, I just wanted to get
place holders and the configure.in checked in.
