avcodec/me_cmp: Mark ff_square_tab as hidden

ff_square_tab is always used with an offset; if this table
is marked as hidden, the compiler can infer that it and
therefore also ff_square_tab + 256 have a fixed offset
from the code. This allows to avoid performing "+ 256"
at runtime by baking it into the offset from the code to
the table.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/me_cmp.h

@@ -21,9 +21,11 @@
 
 #include <stdint.h>
 
+#include "libavutil/attributes_internal.h"
+
 #include "avcodec.h"
 
-extern const uint32_t ff_square_tab[512];
+extern const uint32_t attribute_visibility_hidden ff_square_tab[512];
 
 
 /* minimum alignment rules ;)