Fix net/libbind cross-build on NetBSD.

XXX Needs `.if ${OPSYS} == "NetBSD"' for ac_cv_* settings.

Index: net/libbind/Makefile
===================================================================
RCS file: /cvsroot/pkgsrc/net/libbind/Makefile,v
retrieving revision 1.5
diff -p -u -r1.5 Makefile
--- net/libbind/Makefile	23 Oct 2012 17:18:33 -0000	1.5
+++ net/libbind/Makefile	23 Apr 2013 13:29:19 -0000
@@ -16,6 +16,9 @@ CONFLICTS=		man-pages-[0-9]*
 GNU_CONFIGURE=	yes
 USE_LIBTOOL=	yes
 
+# [TRC 20130326: Kludge for cross-compilation.]
+CONFIGURE_ENV+=		ac_cv_file__dev_random=yes
+
 CONFIGURE_ARGS+=	--with-libtool=yes
 
 MAKE_JOBS_SAFE=	no