posix: POSIX-1.2008 moved SA_* from XSI to base standard

Starting with POSIX-1.2008, "The SA_RESETHAND, SA_RESTART, SA_SIGINFO,
SA_NOCLDWAIT, and SA_NODEFER constants are moved from the XSI option to
the Base." Make them so visible.

PR: 275328
Sponsored by: Netflix

(cherry picked from commit 06af7bd12a4a654f5c5e8da41cf329eee3aa61f6)