backport r1821195 from trunk and add util_debug.c to libhttpd.mak

http://mail-archives.apache.org/mod_mbox/httpd-dev/201801.mbox/%3C4C412873-869D-4A0C-89E6-397706EFA1F7@apachelounge.com%3E



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1821196 13f79535-47bb-0310-9956-ffa450edef68