mknod(2): The required include is <sys/stat.h>, not <unistd.h>.

This is what SUSv4 requires, and also the only thing that works if strict
standards compliance is requested or mknodat() is needed.

PR:		standards/123688
Submitted by:	gcooper
MFC after:	1 week

lib/libc/sys/mknod.2

@@ -28,7 +28,7 @@
 .\"     @(#)mknod.2	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd April 10, 2008
+.Dd January 16, 2011
 .Dt MKNOD 2
 .Os
 .Sh NAME
@@ -38,7 +38,7 @@
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
-.In unistd.h
+.In sys/stat.h
 .Ft int
 .Fn mknod "const char *path" "mode_t mode" "dev_t dev"
 .Ft int