strptime: silence gcc warnings Cross-compiling to mingw raised a couple of gcc warnings. * lib/strptime.c (__strptime_internal) [!_NL_CURRENT], [!_LIBC && !HAVE_TM_GMTOFF]: Avoid unused variables. Reported by Daniel P. Berrange. Signed-off-by: Eric Blake <eblake@redhat.com>