Fix check for jpeg_mem_ to work with libjpeg-turbo

code/renderercommon/tr_image_jpg.c

@@ -37,8 +37,8 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 #include <jpeglib.h>
 
 #ifndef USE_INTERNAL_JPEG
-#  if JPEG_LIB_VERSION < 80
-#    error Need system libjpeg >= 80
+#  if JPEG_LIB_VERSION < 80 && !defined(MEM_SRCDST_SUPPORTED)
+#    error Need system libjpeg >= 80 or jpeg_mem_ support
 #  endif
 #endif