Allow stack limits to be testable

In SERVER-63055, we completely removed halving the stack size on debug builds because it was preventing us from implementing coverage reporting with Clang and it was believed to not be of use anymore. However, jason.carey@mongodb.com points out that its original purpose was to serve as an early detection mechanism for new code that could potentially overflow the stack.

We should re-implement the stack size limitation more explicitly so that it can be tested as a distinct test scenario.