ISO C restricts enumerator values to the range of int. Thus (for instance) 0x80000000
unfortunately does not work, and throws a warning with -Wpedantic on
clang 3.7.

This fixes it by using alternative expressions that result in identical
values but do not have this issue.

Tested with FATE.
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>