sysutils/seatd: fix build on GCC architectures

Disable -Werror:
../seatd/client.c: In function 'get_peer':
../seatd/client.c:49:51: error: operand of ?: changes signedness from 'int' to 'gid_t' {aka 'unsigned int'} due to unsignedness of other operand [-Werror=sign-compare]

49 |  *gid = cred.cr_ngroups > 0 ? cred.cr_groups[0] : -1;
   |                                                   ^~

../seatd/client.c: At top level:
cc1: error: unrecognized command line option '-Wno-unused-command-line-argument' [-Werror]
cc1: error: unrecognized command line option '-Wno-unknown-warning-option' [-Werror]
cc1: all warnings being treated as errors