Add debug_and_release to use separate build dirs

[softins]

Short description of changes
Adds the debug_and_release option to the CONFIG in Jamulus.pro. This tells qmake to generate separate Makefiles for Debug and Release, each using a separate sub-directory (debug/ and release/ respectively) for build-generated files such as *.o and others, instead of building them in the project root.

The user can then invoke make or make release (the default) to build a release version, or make debug (explicitly) to build a debug version.

This debug_and_release option was already the default for Windows builds, but not for other architectures.

It was necessary also to change mac/deploy_mac.sh to search in Makefile.Release instead of Makefile when looking for the value of QMAKE_TARGET.

CHANGELOG: Build: Place build files in separate directories instead of project root.

Context: Fixes an issue?
Fixes #3092

Does this change need documentation? What needs to be documented and how?
Maybe in compilation instructions, if there are any parts that would need to change as a result. Maybe not.

Status of this Pull Request
Ready to test

What is missing until this pull request can be merged?
Review and test

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

[ann0see]

Thanks. This is very nice. Builds on Debian. The old files in the root of a build don't get removed with a make clean, but that's not too bad.
Yes, the COMPILING.md may need a small hint how to build debug.

[softins]

The old files in the root of a build don't get removed with a make clean, but that's not too bad.

Can always switch back to main, then do a make distclean, and then switch back to this branch.

[ann0see]

Approving and tagging needs documentation

[pljones]

What about .gitignore - does that need updating to ignore the subdirs?

What about make distclean - does that remove both directories?

[pljones]

Also, as COMPILING.md is in jamulussoftware/jamulus, updating it should be part of this change.

[softins]

What about .gitignore - does that need updating to ignore the subdirs?

Good catch. I've checked the build trees I saved from the CI (see my commit b047958 to see how I did so in my branch debug-and-release-test), and added a few build directories to .gitignore that were not there before.

What about make distclean - does that remove both directories?

I can't test that, but we don't generate the actions for make distclean; qmake does that itself, so I hope it gets it right!

It may be that it empties the build directories but doesn't remove them. Or maybe it does; I'm not sure.

[softins]

Also, as COMPILING.md is in jamulussoftware/jamulus, updating it should be part of this change.

Just read through it, and can't see anything that needs to change as a result of this PR. Could possibly add a brief note about make release vs make debug, but make already defaults to make release, so the compilation instructions should still be valid anyway.

I'm not sure what debugging features make debug gives you anyway, so couldn't yet say anything useful about it, only that the option exists.

[pljones]

The MacOS changes make me wonder why we do what's done but if it's needed and works, I suppose it's okay.

[pljones]

#3322 raised for documentation.