Ticket 49522 - Fix build issues on F28
    
    Bug Description:  We are randomly get build failures around libldaputil.la
    
        libtool:   error: cannot find the library 'libldaputil.la' or
                          unhandled argument 'libldaputil.la'
    
    Fix Description:  A previous commit introduced one of the issues, this patch
                      is adding libslapd.la to the LIBADD of libldaputil
    
    https://pagure.io/389-ds-base/issue/49552
    
    Reviewed by: mreynolds(one line commit rule)