Works around <https://bugs.gnu.org/40522>.
* build-aux/compile-all.scm (parallel-job-count*): New procedure.
<top level>: Use it instead of 'parallel-job-count'.
* build-aux/compile-all.scm <top level>: Add calls to 'force-output'
in the #:report-load and #:report-compilation procedures. Fixes a
regression introduced in 2890ad332f
whereby compilation output would be buffered, leading to a weird
visual effect.
* build-aux/compile-all.scm (%default-optimizations)
(%lightweight-optimizations): New variables.
(optimization-options): New procedure.
(compile-file*): Use it.