Add support for building Qt 5.15.2

[jcfr]

• Create branch 5.15.2.
• Update README moving 5.15.1 to unmaintained list (Reference branch for Qt 5.15.(1|2), switch default default to 5.15.2 #63)
• Update CI to build 5.15.2
• Update script to support building for Big Sur (Update scripts to support building Qt 5.15.2 for macOS Big Sur #61)

@jamesobutler Do you know what is the status on Azure Pipeline ?

cc: @piiq

[jamesobutler]

@jcfr From my recollection the next steps for the Azure Pipeline work in this repo was that I needed you to go into Settings->Integrations for this repo and make sure you have the Azure Pipeline GitHub app installed with repository access. Can you do that for me?

The Azure Pipeline repo was set up over at https://dev.azure.com/jchrisfillionr/qt-easy-build.

[jamesobutler]

I included d9ae8b8 as part of the new 5.15.2 branch, but azure pipelines reports a build issue https://dev.azure.com/jchrisfillionr/qt-easy-build/_build/results?buildId=2&view=logs&j=0da5d1d9-276d-5173-c4c4-9d4d4ed14fdb&t=8ef82b3b-1feb-5bbd-06f6-b1f7b5467f03

ERROR: Unknown command line option '-no-xinerama'

See QTBUG-89364: Configure -no-xinerama doesn't work

[jcfr]

next steps for the Azure Pipeline work in this repo was that I needed you to go into Settings->Integrations for this repo and make sure you have the Azure Pipeline GitHub app installed with repository access

This should be good now.

ERROR: Unknown command line option '-no-xinerama'

Out of curiosity, is this error new with 5.15.2 ? Was this option available with 5.15.1 but having no effect ?

[jamesobutler]

The original Qt bug report was issued by someone having issues with it using 5.15.1 so I'm guessing it wasn't an option then either. Seems like the documentation was not correct from briefly looking into that text.

When you tried with Qt 5.15.1 as part of #60 did it work?

[jamesobutler]

A more detailed thread about xinerama https://bugreports.qt.io/browse/QTBUG-84749

In general seems like Qt has taken the approach of the user making sure they have certain dependencies. Meaning likely their -no flag hasn’t been maintained and is not working.

[jcfr]

Support for building without xinerama is now tracked in a dedicated issue:

• Revisit support for -no-xinerama associated with Qt 5.15.2 #65