Build lib/ objects in the SConscript variant_dir.

[rryan]

SCons has a feature that lets you declare a repository-root absolute
path to a file (e.g. "#lib/soundtouch/..."). Using this feature
prevents SCons from automatically re-directing built artifacts to a
variant_dir. To work around this, this commit moves src/SConscript and
src/SConscript.env to the root, and changes all paths in SConscripts
to use SConscript-relative paths.

This commit also switches to building an explicit static library for
vamp-hostdk, vamp-sdk, and soundtouch when internal linking is enabled
and the VAMP plugin now uses the system soundtouch if it is present.

Fixes Bug #1191327 and Bug #1617802.

[rryan]

Packaging is almost certainly broken, but this is ready for testing by anyone who is interested.

[rryan]

Windows packaging is ok -- need to test on Ubuntu and macOS.

[rryan]

macOS packaging is ok.

[rryan]

Ubuntu packaging works.

[rryan]

From a fresh checkout, running scons produces the following files now:

$ git status --ignored           
On branch scons

Ignored files:
  (use "git add -f <file>..." to include in what will be committed)

	.sconf_temp/
	.sconsign.branch
	.sconsign.dblite
	build/__init__.pyc
	build/depends.pyc
	build/features.pyc
	build/mixxx.pyc
	build/protoc.pyc
	build/qt5.pyc
	build/util.pyc
	cache/
	config.log
	lin64_build/
	mixxx

And lin64_build is a mirror of the repo (on a system that has soundtouch and vamp installed):

$ tree -L 2 lin64_build
lin64_build
├── lib
│   ├── fidlib
│   ├── hidapi-0.8.0-rc1
│   ├── libebur128
│   ├── portaudio
│   ├── qtscript-bytearray
│   ├── replaygain
│   ├── reverb
│   └── xwax
├── libmixxx.a
├── mixxx
├── res
│   ├── qrc_mixxx.cc
│   └── qrc_mixxx.o
├── src
│   ├── analyzer
│   ├── broadcast
│   ├── build.h
│   ├── control
│   ├── controllers
│   ├── database
│   ├── dialog
│   ├── effects
│   ├── encoder
│   ├── engine
│   ├── errordialoghandler.o
│   ├── library
│   ├── main.o
│   ├── mixer
│   ├── mixxxapplication.o
│   ├── mixxx.o
│   ├── moc_errordialoghandler.cc
│   ├── moc_errordialoghandler.o
│   ├── moc_mixxxapplication.cc
│   ├── moc_mixxxapplication.o
│   ├── moc_mixxx.cc
│   ├── moc_mixxx.o
│   ├── musicbrainz
│   ├── preferences
│   ├── proto
│   ├── recording
│   ├── skin
│   ├── soundio
│   ├── sources
│   ├── track
│   ├── util
│   ├── vinylcontrol
│   ├── waveform
│   └── widget
└── vamp-plugins
    ├── base
    ├── dsp
    ├── ext
    ├── libmain.os
    ├── libmixxxminimal.so
    ├── maths
    └── plugins

[benis]

Saw your comment on Zulip, building from scratch works fine for me on macOS.

[rryan]

Thanks for testing @beenisss!

[benis]

Hmm, I happened to rebuild this via Eclipse just now (used command line previously) and I get this error when it finishes.

I don't know if that's significant.

[rryan]

@beenisss I'm not sure what that error indicates on the SCons side. @daschuer do you have any ideas?

[benis]

I think you can chalk this up to some transient blip on my local machine, I've been getting some weird inconsistent behaviour with building and cleaning lately. Just tried this again and didn't get the error.

[rryan]

I think this change is ready to go, I've personally tested on windows/macos/linux and @beenisss tested on macos.

[rryan]

Any objections? I'd like to merge this so I can stop having to rebase :).

[Be-ing]

Will test soon

[Be-ing]

Is there any particular reason we put the OS name in the build directory name? Why not just call the directory build like is conventional with CMake?

[rryan]

I'm not sure, I think if you switch between 32-bit and 64-bit builds on the same checkout it could be handy and @Pegasus-RPG has done that in the past. But I don't think the OS name needs to be there.

[Be-ing]

Works for me 👍

[rryan]

Works for me 👍

Thanks for testing!