Rebuild native executable when changes to the build system are made
When the build rules needs to be updated, cmake isn't always rerun for the native build.
This adds a dependency file that ensures it does. This feature is limited to cmake, so there are no changes with other build systems and a call to clean might still be necessary.
ninja ninja # Check native build isn't ran again. touch build.ninja ninja # Native build runs again.
Build with make as a generator and verify it's still good.
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D5624