Fix libevent requiring <net/if.h>.

ports/libevent/libevent.patch

@@ -81,6 +81,33 @@ diff -Paur --no-dereference -- libevent.upstream/configure libevent/configure
    ;
    return 0;
  }
+diff -Paur --no-dereference -- libevent.upstream/evutil.c libevent/evutil.c
+--- libevent.upstream/evutil.c
++++ libevent/evutil.c
+@@ -76,8 +76,10 @@
+ #include <time.h>
+ #include <sys/stat.h>
+ #ifndef _WIN32
++#if __has_include(<net/if.h>)
+ #include <net/if.h>
+ #endif
++#endif
+ #ifdef EVENT__HAVE_IFADDRS_H
+ #include <ifaddrs.h>
+ #endif
+@@ -2007,7 +2009,12 @@
+ 	if (cp == NULL)
+ 		return evutil_inet_pton(af, src, dst);
+ 
++#if __has_include(<net/if.h>)
+ 	if_index = if_nametoindex(cp + 1);
++#else
++	if_index = 0;
++	errno = ENODEV;
++#endif
+ 	if (if_index == 0) {
+ 		/* Could be numeric */
+ 		if_index = strtoul(cp + 1, &check, 10);
 diff -Paur --no-dereference -- libevent.upstream/evutil_rand.c libevent/evutil_rand.c
 --- libevent.upstream/evutil_rand.c
 +++ libevent/evutil_rand.c