assert.3: ATTRIBUTES: Note function that is thread-safe

It's marking matches glibc marking.

Signed-off-by: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/assert.3

@@ -56,6 +56,19 @@ The message "assertion failed in file foo.c, function
 do_bar(), line 1287" is of no help at all to a user.
 .SH RETURN VALUE
 No value is returned.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lb lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.BR assert ()
+T}	Thread safety	MT-Safe
+.TE
+
 .SH CONFORMING TO
 POSIX.1-2001, C89, C99.
 In C89,