Fixed bug 4003 - HAVE_POLL undefined in SDL_poll.c, making it impossible to use.

tomwardio

HAVE_POLL is correctly defined in SDL_config.h when running configure. However, in the only place where it's used, it's undefined at the start of the file.

src/core/unix/SDL_poll.c

@@ -24,7 +24,6 @@
 #include "SDL_assert.h"
 #include "SDL_poll.h"
 
-#undef HAVE_POLL
 #ifdef HAVE_POLL
 #include <poll.h>
 #else