mod_cgi: Restore logging of stderr from child process when ScriptLog

isn't used (as in 1.3), except that on Unix it is now logged via
ap_log_rerror() instead of by the child having STDERR_FILENO refer
to the error log.
Submitted by:	Greg Ames
Reviewed by:	Jeff Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85331 13f79535-47bb-0310-9956-ffa450edef68