Correctly pass through flags `rb_process_status_wait`.

[ioquatix]

rb_process_status_wait is not exposed yet in CRuby, but when/if it is, it will take a flags argument.

WNOHANG should always be set, as it's used to (efficiently) by-pass the fiber scheduler.

Types of Changes

• Bug fix.
• New feature.
• Maintenance.

Contribution

• [ ] I added tests for my changes.
• [x] I tested my changes locally.
• [x] I agree to the Developer's Certificate of Origin 1.1.

[ioquatix]

See https://github.com/ruby/ruby/pull/8316 for more context.