[monero-project/monero] One build directory per branch/arch. (#4286)

If these changes are beneficial for monero, than moneroexamples can be adopted to this change. However, I don’t know how this change will propagate when checking out older monero releases, which I often do?

For example if I make new branch based on v12.3.0 (`git checkout -b last_release v0.12.3.0`) and compile this new branch to have v0.12.3 monero libraries, this new build directory scheme obviously will not be used. And this complicate things, at least till the new scheme will be made official with next monero release.