Use SDL_main on all platforms.
Fix main() for non-const argv so it matches with the SDL
prototype.
Adapt win32 WinMain() to main() and get rid of the win32 special
case in Common::Init().
Don't include the lazy precompiled.h everywhere, only what's
required for the compilation unit.
platform.h needs to be included instead to provide all essential
defines and types.
All includes use the relative path to the neo or the game
specific root.
Move all idlib related includes from idlib/Lib.h to precompiled.h.
precompiled.h still exists for the MFC stuff in tools/.
Add some missing header guards.
Detect CPU features at runtime via cpuid - code borrowed from
libavutil.
Availability of cpuid is not checked since pentium3 supports it
and that was the minimum requirement anyway.
Only features enabled at compile time will be available.
Forced MMX/SSE/SSE2/SSE3 and it passed all tests via:
./doom3.x86_64 +disconnect +set s_noSound 1 +testSIMD
Thread return types are different between platforms, and its
probably not a good idea to return something of a different size,
cast the callback and expect it to not crash.
