multiprocessing.eclass: change default inf to nproc + distutils-r1 pbr build system

[mgorny]

CC @gentoo/qa

From the relevant commit:

Change the default value for 'inf' argument to makeopts_jobs from 999
to $(get_nproc). This means that if MAKEOPTS specifies a -j argument
without a specific value, nproc will be used rather than infinity-ish
number of jobs.

The old default made sense for ebuilds using both makeopts_jobs
and makeopts_loadavg. However, these are very rare — only 4 packages
and 3 eclass at this time. For the remaining ebuilds, they meant
uncontrollably using up to 999 jobs.

The new default is both safer and more correct for the vast majority
of Gentoo packages, removing the necessity of repeating:

$(makeopts_jobs "${MAKEOPTS}" "$(get_nproc)")

The ebuilds and eclasses using makeopts_loadavg have been updated
to pass the old default.

Also includes tiny distutils-r1 change to avoid updating the cache twice.

[mgorny]

CC @gentoo/kde for cmake*, @floppym for ninja-utils

[gentoo-bot]

Pull Request assignment

Submitter: @mgorny
Areas affected: ebuilds, eclasses
Packages affected: app-i18n/mozc, dev-python/fixtures, dev-qt/qtwebengine, dev-util/cmake, media-sound/apulse

app-i18n/mozc: @Arfrever, @gentoo/cjk
dev-python/fixtures: @prometheanfire, @gentoo/python
dev-qt/qtwebengine: @gentoo/qt, @gyakovlev
dev-util/cmake: @gentoo/base-system, @gentoo/kde
media-sound/apulse: @bircoph

Linked bugs

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[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2022-04-28 11:23 UTC
Newest commit scanned: 9a72dbc
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
https://qa-reports.gentoo.org/output/gentoo-ci/672f8b0566/output.html

[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2022-04-28 13:53 UTC
Newest commit scanned: fac121c
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
https://qa-reports.gentoo.org/output/gentoo-ci/2a5ac41a1d/output.html