* misc/sys/syslog.h: Include <bits/syslog.h> for fortification.
* misc/Makefile (headers): Add bits/syslog.h.
* include/sys/syslog.h: Add __vsyslog_chk prototype and hidden_proto.
* sysdeps/generic/syslog.c: Change vsyslog function to __vsyslog_chk.
Call __vfprintf_chk if necessary. Make vsyslog a wrapper. Add
__syslog_chk.
* misc/Versions: Export __syslog_chk and __vsyslog_chk.
* nis/nis_xdr.c: Help gcc to avoid generating unnecessary wrapper
functions.