Include <locale.h> to avoid error: 'LC_ALL' undeclared.
When compiling ZFS with CFLAGS=-O0 it will trigger the following error.
Resolve the issue by properly including locale.h.
../../cmd/mount_zfs/mount_zfs.c: In function 'main': ../../cmd/mount_zfs/mount_zfs.c:318:2: warning: implicit declaration of function 'setlocale' [-Wimplicit-function-declaration] ../../cmd/mount_zfs/mount_zfs.c:318:19: error: 'LC_ALL' undeclared (first use in this function)
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #724