closes https://github.com/assimp/assimp/issues/1655: add typedef for android NDK.

contrib/zlib/zlib.h

@@ -77,6 +77,9 @@ extern "C" {
   the consistency of the compressed data, so the library should never crash
   even in the case of corrupted input.
 */
+#ifdef __ANDROID__     
+using zcrc_t = unsigned_long; 
+#endif
 
 typedef voidpf (*alloc_func) OF((voidpf opaque, uInt items, uInt size));
 typedef void   (*free_func)  OF((voidpf opaque, voidpf address));