o Add pthread_yield.3 man page.

PR:		docs/100083
Reviewed by:	deischen, ru
Obtained from:	OpenBSD
MFC after:	2 weeks

share/man/man3/Makefile

@@ -208,7 +208,8 @@ PTHREAD_MAN=	pthread.3 \
 		pthread_suspend_all_np.3 \
 		pthread_suspend_np.3 \
 		pthread_switch_add_np.3 \
-		pthread_testcancel.3
+		pthread_testcancel.3 \
+		pthread_yield.3
 
 PTHREAD_MLINKS=	pthread_attr.3 pthread_attr_destroy.3 \
 		pthread_attr.3 pthread_attr_getdetachstate.3 \

share/man/man3/pthread_yield.3

@@ -0,0 +1,31 @@
+.\" $OpenBSD: pthread_yield.3,v 1.3 2004/01/25 14:48:32 jmc Exp $
+.\"
+.\" PUBLIC DOMAIN: No Rights Reserved. Marco S Hyman <marc@snafu.org>
+.\"
+.\" $FreeBSD$
+.\"
+.Dd September 18, 2006
+.Dt PTHREAD_YIELD 3
+.Os
+.Sh NAME
+.Nm pthread_yield
+.Nd yield control of the current thread
+.Sh LIBRARY
+.Lb libpthread
+.Lb libthr
+.Sh SYNOPSIS
+.In pthread.h
+.Ft void
+.Fn pthread_yield void
+.Sh DESCRIPTION
+The
+.Fn pthread_yield
+forces the running thread to relinquish the processor until it again
+becomes the head of its thread list.
+.Sh SEE ALSO
+.Xr sched_yield 2
+.Sh STANDARDS
+The
+.Fn pthread_yield
+is a non-portable (but quite common) extension to
+.St -p1003.1-2001 .