core: use strncmp in check_errorlog_dir and core_dump_config when checking

if the ErrorLog directive is configured with the 'syslog' prefix. PR 62102

trunk patch: none, as far as I can see the code in trunk diverged too much
          due to the code in STALLED for ap_errorlog_provider.
 
Submitted by: elukey, jhriggs, jailletc36
Reviewed by: elukey, jhriggs, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1832493 13f79535-47bb-0310-9956-ffa450edef68