Fixed bug 3011 - pthread/SDL_syssem.c requires _GNU_SOURCE
Ozkan Sezer
pthread/SDL_syssem.c requires _GNU_SOURCE predefined (like SDL_sysmutex.c),
otherwise sem_timedwait() prototype might not be available to it. Problem
seen with glibc-2.3.4.
Windows: Always set the system timer resolution to 1ms by default.
An existing hint lets apps that don't need the timer resolution changed avoid
this, to save battery, etc, but this fixes several problems in timing, audio
callbacks not firing fast enough, etc.
Fixes Bugzilla #2944.