apply altivec fixes from Emanuel Steen (#2383)

code/renderer/tr_surface.c

@@ -21,6 +21,9 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 // tr_surf.c
 #include "tr_local.h"
+#if idppc_altivec
+#include <altivec.h>
+#endif
 
 /*