erf.3: Add a STANDARDS section

Add a STANDARDS section for the erf(3) manual page.

PR:	273413
Reviewed by:	pauamma_gundo.com
Differential Revision:	https://reviews.freebsd.org/D44140

(cherry picked from commit 16c3d7e1fa)

lib/msun/man/erf.3

@@ -25,9 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"     from: @(#)erf.3	6.4 (Berkeley) 4/20/91
-.\"
-.Dd July 13, 2014
+.Dd June 23, 2024
 .Dt ERF 3
 .Os
 .Sh NAME
@@ -88,6 +86,17 @@ subtracts the result of the error function
 from 1.0.
 .Sh SEE ALSO
 .Xr math 3
+.Sh STANDARDS
+The
+.Fn erf ,
+.Fn erff ,
+.Fn erfl ,
+.Fn erfc ,
+.Fn erfcf
+and
+.Fn erfcl
+functions conform to
+.St -isoC-99 .
 .Sh HISTORY
 The
 .Fn erf