Define JACK headers and sources globally and add some documentation

[ann0see]

Short description of changes
Instead of using hardcoded paths to the sound files @pgScorpio suggested to use variables. This PR uses global definitions for JACK sources and headers and adds some small comments.

CHANGELOG: Internal: Improved maintainability of Jamulus.pro by using global definitions.

Context: Fixes an issue?
Fixes: #2573

Does this change need documentation? What needs to be documented and how?
No

Status of this Pull Request
Ready for testing

What is missing until this pull request can be merged?
Needs whole CI to pass

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want (Linux (JACK gives no warning and sound is OK), Windows too. I can't test macOS at the moment - but build is OK.)
• 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

AUTOBUILD: Please build all targets

[pljones]

I'd split this into two parts:

• provided by the SDK
• "part of Jamulus"

[pljones]

I'd also make all the variable definitions be either

VARNAME =

or

VARNAME = value

depending on the config that makes them relevant.

[ann0see]

Done

[pljones]

Done

I'm not sure if you misunderstood or forgot a commit here but this doesn't look to have done what I suggested.

[ann0see]

Hmm. Then I misunderstood you. I thought you were referring to splitting the ASIO part out to another variable? Can you please provide a suggestion what you'd like to see?

[pljones]

Should line 97 be done more like

SOURCES_OBOE = src/sound/oboe/sound.cpp
# TODO: Remove debugging code if no longer needed else move to src/sound if part of sound
SOURCES_OBOE += src/android/androiddebug.cpp

[ann0see]

Ok. Yes. Done.

[pljones]

I'm starting to think this is creating a lot of variables for no benefit.

The variables should only be added to the overall HEADERS, etc, variables conditionally - so wouldn't it be better to do this (addding the headers, etc, separately) where that conditional adding of the variables is done?

[ann0see]

@pljones so you mean basically that we should revert this? I think @pgScorpio mainly wanted to get rid of the duplication introduced by the JACK headers.

[pljones]

@pljones so you mean basically that we should revert this? I think @pgScorpio mainly wanted to get rid of the duplication introduced by the JACK headers.

Are the variables used in multiple places? Otherwise there's no duplication being removed.

[ann0see]

The JACK headers are used for all three main OS.

[pljones]

The JACK headers are used for all three main OS.

OK, so it's probably best done just for the JACK values, right?

[ann0see]

@pljones I've now updated my PR and split it into two commits. I hope that's ok for all.

[pljones]

Looks good.