It is superceeded by the #[no_core] attribute

`make check` executes `tidy` after compile. It reminds me that I've left
long lines or trailing whitespaces only after compilation finshed. That
is too late since I have to recompile only because fixing the trivial
formatting issues.

Run tidy first to avoid potentially unnecessary re-compilation.

Issue #1419

This should allow a small speedup for test builds; unset by default