Compile on Erlang/OTP 21

[michaelklishin]

Proposed Changes

This is one of the PRs that makes RabbitMQ build successfully on Erlang/OTP 21.

OTP 21 deprecated erlang:get_stacktrace/0 in favor of a new try/catch syntax. Unfortunately that's not realistic for projects that support multiple Erlang versions (like us) until OTP 21 can be the minimum version requirement. In order to compile we have to ignore the warning. The broad compiler option seems to be the most common way to support compilation on multiple OTP versions with warnings_as_errors: if we use a function-specific option it will fail on the releases where the function is not deprecated.

Types of Changes

• [x] Bug fix (non-breaking change related to https://github.com/rabbitmq/rabbitmq-server/issues/1616)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation (correction or otherwise)
• [ ] Cosmetics (whitespace, appearance)

Checklist

• [x] I have read the CONTRIBUTING.md document
• [x] I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• [ ] All tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)
• [ ] Any dependent changes have been merged and published in related repositories

Further Comments

[#157964874]