Fix mach handler imports

[kattrali]

Goal

Restore mach handler to full functionality. There was a missing import which led to an undefined define which was required, causing fallback to the signal handler in situations where more debugging information was available.

Tests

• Manually verified by raising signals, and causing C++/NS exceptions with a custom handler which did not call previous handler. All of these cases are captured correctly and send a single report
• Automated integration tests

Review

For the submitter, initial self-review:

• Reviewed the test cases added for completeness and possible points for discussion
• A changelog entry was added for the goal of this pull request
• Check the scope of the changeset - is everything in the diff required for the pull request?
• This pull request is ready for final review

For the pull request reviewer(s), this changeset has been reviewed for:

• Consistency across platforms for structures or concepts added or modified
• Consistency between the changeset and the goal stated above
• Internal consistency with the rest of the library - is there any overlap between existing interfaces and any which have been added?
• Usage friction - is the proposed change in usage cumbersome or complicated?
• Performance and complexity - are there any cases of unexpected O(n^3) when iterating, recursing, flat mapping, etc?
• Concurrency concerns - if components are accessed asynchronously, what issues will arise
• Thoroughness of added tests and any missing edge cases
• Idiomatic use of the language