gethostid.3: ATTRIBUTES: Note functions that are/aren't thread-safe

The markings match glibc markings.
markings of functions in glibc are:
- gethostid: MT-Safe hostid env locale
- sethostid: MT-Unsafe const:hostid

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/gethostid.3

@@ -89,6 +89,22 @@ to store the host ID.
 .B EPERM
 The calling process's effective user or group ID is not the same
 as its corresponding real ID.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lb lb lbw25
+l l l.
+Interface	Attribute	Value
+T{
+.BR gethostid ()
+T}	Thread safety	MT-Safe hostid env locale
+T{
+.BR sethostid ()
+T}	Thread safety	MT-Unsafe const:hostid
+.TE
+
 .SH CONFORMING TO
 4.2BSD; these functions were dropped in 4.4BSD.
 SVr4 includes