Linux SDK support for building Natron 2.6 with QT5

[pwnage101]

What type of PR is this? (Check one of the boxes below)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which does not add functionality nor fixes a bug but improves Natron in some way)
• Breaking change (fix or feature that would cause existing functionality to change)
• My change requires a change to the documentation
  • I have updated the documentation accordingly

What does this pull request do?

Update the SDK to support building Natron 2.6 for Linux.

Have you tested your changes (if applicable)? If so, how?

TBD

Futher details of this pull request

Depends on:

• OpenEXR/IlmBase 2.x -> OpenEXR/Imath 3.x openfx-io#53

Related issues:

• Natron 2.6 (Qt5) binary distrib for Linux #741
• [HELP NEEDED] Prepare Linux binary distrib of Natron 2.6 #990

[pwnage101]

Can't promise anything, but I really wanted Natron 2.6 running on linux. Still working out the kinks. TODO:

• pyside2/shiboken2 are still installed via apt instead of compiled. Fix this to make them not come from a specific distro package manager.
• imath.sh is experimental---test it.
• remove python 2 support

[pwnage101]

qtlocation under QT5 does not compile with GCC 13.x. I think this is fixed in newer versions of QT, but it doesn't matter because I don't think Natron uses qtlocation. More info: https://bugreports.qt.io/browse/QTBUG-113111

[pwnage101]

Spent a cumulative 40 hours on getting a working SDK built with fully compiled dependencies, but ultimately gave up after struggling with compiling pyside2/shiboken2 and ultimately failing.

I'm trying something new with an ubuntu-based SDK where all dependencies are installed via apt and making much more progress so far.

[rodlie]

I'm trying something new with an ubuntu-based SDK where all dependencies are installed via apt and making much more progress so far.

Forget about Ubuntu. We build our own depends on CentOS/EL for a reason.

It should not be hard to add Qt5 to the existing build infrastructure.