mem: Fix usage of memalign() on DJGPP.

Credits to Khusraw of bttr-software.de forum.
Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>

libavutil/mem.c

@@ -95,7 +95,11 @@ void *av_malloc(size_t size)
 #elif HAVE_ALIGNED_MALLOC
     ptr = _aligned_malloc(size, ALIGN);
 #elif HAVE_MEMALIGN
+#ifndef __DJGPP__
     ptr = memalign(ALIGN, size);
+#else
+    ptr = memalign(size, ALIGN);
+#endif
     /* Why 64?
      * Indeed, we should align it:
      *   on  4 for 386