globally (effectively) --catch_system_errors=no all boost-test based unit tests

[spoonincode]

Some of our tests require --catch_system_errors=no to properly operate, but there is another compelling reason to blanket this option on all tests: gathering core dumps. Default behavior (--catch_system_errors=yes) will block core dump creation for those tests should they fail. Instead of needing to remember to sprinkle --catch_system_errors=no in all the various add_test() declarations (prone to missing some), we have some other options,

• set BOOST_TEST_CATCH_SYSTEM_ERRORS environment variable in CI. This allows CI to gobble up core dumps from any test, but introduces a difference in CI vs non-CI behavior
• plumb the option in boost test's C++ initialization (but this requires manual plumbing for every test)
• set the BOOST_TEST_DEFAULTS_TO_CORE_DUMP preprocessor macro
  • Secondary option: plumb through a new INTERFACE library that depends on Boost::unit_test_framework to add BOOST_TEST_DEFAULTS_TO_CORE_DUMP; but this still requires remembering in every place we use boost test we need to link to leap_boost_unit_test instead of Boost::unit_test_framework

As much as I detest "global" cmake compile definitions, the BOOST_TEST_DEFAULTS_TO_CORE_DUMP preprocessor macro seems the best option in terms of being a single location with consistent blanket behavior. Certainly open to opinions though.

Work on #640

[heifner]

I've always considered default behavior of --catch_system_errors=yes to be an anti-feature.