This allows information to be gathered while debugging while also
supporting running the test suite with the debugging enabled to test
CMake module changes without tripping `stderr` output checkers.
This provides a utility macro which prints out:
- location of the call;
- the expression being evaluated; and
- the value of the expression.
Evaluates to the value of the expression.
Inspired by Rust's `dbg!` macro.
See: https://doc.rust-lang.org/stable/std/macro.dbg.html