Ticket 49601 - Replace HAVE_SYSTEMD define with WITH_SYSTEMD in svrcore
    
    Bug Description: As former configure of svrcore is not used after the
    merge of svrcore, and the svrcore's --with-systemd configure flag
    handling seems to not have been merged to the 389-ds-core configure,
    and configuring svrcore --with-systemd defines HAVE_SYSTEMD which is
    different from define WITH_SYSTEMD used in 389-ds-base, the systemd
    support in svrcore is not effectively turned on when compiling
    389-ds-base with --with-systemd.
    
    Fix Description: Use the very same define as 389-ds-base
    uses (WITH_SYSTEMD) instead of the former one of svrcore, which is
    obviously inheritted into the svrcore code as well, thus effectively
    selecting a code to be compiled based on the --with-systemd configure
    flag.
    
    https://pagure.io/389-ds-base/issue/49601
    
    Author: mhonek
    
    Review by: mreynolds, spichugi