configure: check for luaL_register in liblua

This is a temporary workaround for a missing compatibility API on
Debian-like systems (and anyone else who doesn't compile with
LUA_COMPAT_MODULE). Ignore any such libraries so we don't fail
confusingly later.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1785753 13f79535-47bb-0310-9956-ffa450edef68