Backport:

mod_sed: Don't define PATH_MAX to a potentially undefined value, causing
compile problems on GNU hurd.
Submitted by: sf
Reviewed by: minfrin, fuankg


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1305822 13f79535-47bb-0310-9956-ffa450edef68