Rationale:
- it is advised to use max-jobs and num-cpus with the same value in wiki
- max-jobs was used only for lcms2 and few gbuild
  modules outside of tail_build anyway.

Also fixes:
- really use CHECK_PARALLELISM when meant to
- EXTMAXPROCESS is not defined in gbuild;
  use parent's jobservers in sub-make where possible

Change-Id: I501de732d223ce0c935081bd1d73da611d16ee88
Reviewed-on: https://gerrit.libreoffice.org/930Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>