fix: openldap does not use Fedora build flags
    
    - %configure introduces the correct flags, however we need* to set our
      custom CFLAGS before the actual run of ./configure, thus we request
      the flags explicitly using %set_build_flags
    - dropping %{optflags} which is just a legacy version of
      %{build_cflags} which is already included in $set_build_flags set
    
    * ./configure plays with the flags, hence customizing the CFLAGS after
      %configure does not have a desired effect
    
    Resolves: #1548676