wdctl: fix conflicting types on old systems

wdctl: fix conflicting types on old systems

The program wants the userland version of declaration(s), not the
kernel one.  Problem occured with glibc-devel-2.5-34.

/usr/include/stdint.h:41: error: conflicting types for 'int64_t'
/usr/include/linux/types.h:98: error: previous declaration of 'int64_t' was here
/usr/include/stdint.h:56: error: conflicting types for 'uint64_t'
/usr/include/linux/types.h:96: error: previous declaration of 'uint64_t' was here
In file included from /usr/include/stdlib.h:438,
                 from ./include/c.h:13,
                 from sys-utils/wdctl.c:30:

Signed-off-by: Sami Kerola <kerolasa@iki.fi>