AC_CHECK_HEADERS with no args causes autoconf to generate a shell for loop

with nothing to iterate over, which some shells don't like. Patch it out.
Fixes PR 40415. Build fix only; no version change.

net/libpcap/distinfo

@@ -1,7 +1,9 @@
-$NetBSD: distinfo,v 1.22 2008/10/30 16:35:08 tron Exp $
+$NetBSD: distinfo,v 1.23 2009/05/17 22:28:51 dholland Exp $
 
 SHA1 (libpcap-1.0.0.tar.gz) = 9893654027ae11033d785045ff35583da43fe8fa
 RMD160 (libpcap-1.0.0.tar.gz) = 20857fe6af5dc70fffb19da46e0fee908f55b3ea
 Size (libpcap-1.0.0.tar.gz) = 524273 bytes
 SHA1 (patch-aa) = 2bf7bef9e114db7ee9e7d6e5facc8f314969f703
 SHA1 (patch-ac) = 6066b492fc82ee149608b8ab3c28c6cef4752976
+SHA1 (patch-ad) = 3f9c535b522a13f74a1363f56332ef1a8db9c77a
+SHA1 (patch-ae) = 862f292a91f9acc489fee5e7136df2cbaf386269

net/libpcap/patches/patch-ad

@@ -0,0 +1,16 @@
+$NetBSD: patch-ad,v 1.3 2009/05/17 22:28:51 dholland Exp $
+
+Remove bogus check that generates invalid shell syntax in the output.
+
+Upstream: already fixed in upstream git.
+
+--- configure.in.orig	2009-05-17 18:18:27.000000000 -0400
++++ configure.in	2009-05-17 18:18:38.000000000 -0400
+@@ -358,7 +358,6 @@ linux)
+ #include <net/if.h>
+ #include <linux/types.h>
+ 	])
+-	AC_CHECK_HEADERS()
+ 	AC_LBL_TPACKET_STATS
+ 	AC_LBL_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI
+ 	;;

net/libpcap/patches/patch-ae

@@ -0,0 +1,19 @@
+$NetBSD: patch-ae,v 1.3 2009/05/17 22:28:51 dholland Exp $
+
+Avoid invalid shell syntax.
+
+Upstream: already fixed in upstream git.
+
+--- configure.orig	2009-05-17 18:18:32.000000000 -0400
++++ configure	2009-05-17 18:18:45.000000000 -0400
+@@ -6655,8 +6655,9 @@ fi
+ 
+ done
+ 
+-	for ac_header in
++	for ac_header in fnord
+ do
++break;
+ as_ac_Header=`echo "ac_cv_header_$ac_header" | $as_tr_sh`
+ if { as_var=$as_ac_Header; eval "test \"\${$as_var+set}\" = set"; }; then
+   { echo "$as_me:$LINENO: checking for $ac_header" >&5