Try to fix travis osx build, osx does not have getdtablecount() either

pxyconn.c

@@ -776,10 +776,24 @@ pxy_log_dbg_disconnect_child(pxy_conn_child_ctx_t *ctx)
 	}
 }
 
-#ifdef __linux__
+#if defined(__linux__) || defined(__APPLE__)
 /*
  * Copied from:
  * https://github.com/tmux/tmux/blob/master/compat/getdtablecount.c
+ * 
+ * Copyright (c) 2017 Nicholas Marriott <nicholas.marriott@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 int
 getdtablecount()
@@ -797,7 +811,7 @@ getdtablecount()
 	globfree(&g);
 	return n;
 }
-#endif /* __linux__ */
+#endif /* defined(__linux__) || defined(__APPLE__) */
 
 unsigned char *
 pxy_malloc_packet(size_t sz, pxy_conn_ctx_t *ctx)