https://github.com/nmap/nmap/pull/2763
https://bugs.gentoo.org/920712
--- a/libdnet-stripped/config/acinclude.m4
+++ b/libdnet-stripped/config/acinclude.m4
@@ -201,6 +201,8 @@
 dnl
 AC_DEFUN(AC_DNET_IOCTL_ARP,
     [AC_MSG_CHECKING(for arp(7) ioctls)
+    AC_PROG_EGREP
+    AC_PROG_CPP
     AC_CACHE_VAL(ac_cv_dnet_ioctl_arp,
 	AC_EGREP_CPP(werd, [
 #	include <sys/types.h>
--- a/libdnet-stripped/configure.in
+++ b/libdnet-stripped/configure.in
@@ -211,7 +211,7 @@
 AC_REPLACE_FUNCS(err strlcpy strsep)
 
 dnl Checks for other system-specific jonks.
-if test "$CYGWIN" != yes ; then
+AS_IF([test "$CYGWIN" != yes], [
 	AC_DNET_BSD_BPF
 	AC_DNET_LINUX_PROCFS
 	AC_DNET_LINUX_PF_PACKET
@@ -221,7 +221,7 @@
 	AC_DNET_RAWIP_HOST_OFFLEN
 	AC_DNET_RAWIP_COOKED
 	AC_DNET_GETKERNINFO
-fi
+])
 
 dnl Check for arp interface.
 if test "$ac_cv_header_Iphlpapi_h" = yes ; then