Configurations/unix-Makefile.tmpl: Ensure that md-nits always works
The body of the "md-nits" Makefile target assumed an in source build tree.
This change ensures that it works correctly when called from an out-of-source
build tree as well.
Reviewed-by: Paul Dale <pauli@openssl.org> Reviewed-by: Tomas Mraz <tomas@openssl.org> Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/22240)