Add switch `--keep-going`

***In GitLab by @mrchapp on Apr 13, 2023, 16:22 GMT+1:***

The `--keep-going` flag in `make` is useful when we want to see the full extent of the breakage. Sometimes, the build stops very shortly after the first failure, but it really varies due to threading and timing, and this covers the other failures on the current source code.

For the sake of future analysis and bisections, sometimes it's important run `make` with `--keep-going` so that all failures and warnings are listed.

*Migrated from GitLab: https://gitlab.com/Linaro/tuxmake/-/issues/201*

Start by locating the command-line option handling and the code that invokes make. Add the --keep-going switch so make continues after failures and reports all failures and warnings, then verify the build command uses the option when requested.

Written by the indexing model from the issue text.