posix: implement `sigsuspend()`

[ycsin]

This is part of the See POSIX Roadmap for LTSv3 (RFC #51211).

sigsuspend() is required as part of POSIX_SIGNALS Subprofiling Option Group.

For more information, please refer to https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigsuspend.html