This was obtained by setting up this environment:
guix shell -D guix --with-input=guile@3.0.9=guile-next \
--with-commit=guile-next=e2ed33ef0445c867fe56c247054aa67e834861f2
-- make -j5
then adding 'unused-module' to (@@ (guix build compiler) %warnings),
building, and checking all the "unused module" warnings and removing
those that were definitely unused.
* guix/build/guile-build-system.scm (invoke-each)[processes]: New
variable.
[wait-for-one-process]: Check PROCESSES and update it.
[fork-and-run-command]: Update PROCESSES.
* guix/build/guile-build-system.scm (build): Use invoke-each, instead of
for-each, to use multiple cores if available.
(invoke-each, report-build-process): New procedures.
