Check if yasm supports a nasm-specific syntax we use (it doesn't in 0.5.0, which is still common in Linux distros, and does in 0.6.0). Disable it if we don't, attempting to fallback to using nasm. Thanks to Mike Frysinger for the patch. Fixes Bugzilla #393.

/* Include the SDL main definition header */
#include "SDL_main.h"

#ifdef main
#undef main
int main(int argc, char *argv[])
{
	return(SDL_main(argc, argv));
}
#else
/* Nothing to do on this platform */
#endif