Replace --flush-on-signal <int> with --forward-signal <int> in timem

[hidmic]

Follow-up to #225. Turns out that:

• on Linux, components such as cpu_util (see times man pages) and peak_rss (see getrusage man pages) depend on children processes being waited on.
• --flush-on-signal <int> may result in children processes becoming zombie processes if timem gets the signal but its process group does not or children processes do not terminate on that signal.

This patch simply ensures the signal is forwarded. Whether children processes terminate or not it's up to their implementation. When they do, timem properly finishes waiting on them.

[hidmic]

Aha! Thanks for 3d05af8. Where's the linter configuration? I did look for it but could not find it.

[jrmadsen]

All the formatting checks are in .github/workflows/formatting.yml. If you have clang-format-9 installed, you can just "build" the format target and it will run clang-format on the source code. The only thing to watch out for is different versions of clang-format can occasionally cause slightly different formatting changes and then cause the formatting checks to fail.

[jrmadsen]

It looks like the CircleCI build is failing bc of an unrelated issue with the gotcha include directories inside the container this runs in so I am going to merge.