Add runtime --enable-sigint option

[roystgnr]

It's useful to be able to still get a stack trace and PerfLog output after Ctrl+C.

[moosebuild]

Job Coverage, step Generate coverage on 0ba266f wanted to post the following:

Coverage

Mutiple base shas were found when retrieving head reports:
3256228
707101d
Failed to generate the full coverage report

This comment will be updated on new commits.

[moosebuild]

Job Coverage, step Verify coverage on 0ba266f wanted to post the following:

The following coverage requirement(s) failed:

• Failed to generate coverage rate (required: 55.0%)

[jwpeterson]

Failures here look unrelated to the changes. And I guess there's no way to have a test for this, so we'll just have to take your word for it :)