upgraded Qt to 5.12.11 without cherry-picking - bitcoin fixes this (by copy-paste)

[fmhc]

Can build depends & core with upgraded Qt 5.12.11 on Ubuntu 20.04. Instead of fine selected git cherry-picks which would involve switching to a newer build, i just got the new stuff from the bitcoins in and got this flight-ready... My tests:

[fmhc]

https://github.com/dogecoin/dogecoin/pull/2339 this was the PR before, had to start over - multiple times and in the end gave up cherry-picking through 60+ commits and keeping out a change of the build system i guess.

[rnicoll]

Thanks for this! I do want to get this to build on Gitian before we merge, and currently I get the following error on Gitian:

ERROR: Feature 'c++1z' was enabled, but the pre-condition 'features.c++14 && tests.c++1z' failed.
make: *** [/home/ubuntu/build/dogecoin/depends/work/build/x86_64-apple-darwin11/qt/5.12.11-4e56e558921/./.stamp_configured] Error 3
make: Leaving directory `/home/ubuntu/build/dogecoin/depends'

If you have ideas, please do take a look, or I can take a look at this next week.

[patricklodder]

removed from 1.14.4 target milestone, qt (and openssl) dependency updates will have to target 1.14.5

[rnicoll]

I think we can postpone to 1.14.6 or leave for 1.21 to resolve, presuming #2595 resolves #2338

[rnicoll]

Rebased as https://github.com/rnicoll/dogecoin/tree/issue-2339-upgrade-qt-to-5.12.11-nocherrypicking - will see if it passes CI this time, but that's a blocker for reviewing

[patricklodder]

I think this won't work - no OpenSSL. This should be doable now with openssl 1.0.2u - I have some code just haven't touched it yet (I'm currently working on https://github.com/dogecoin/dogecoin/discussions/2624#discussioncomment-1509897 and just started SSE2 work, so this would be something I can pick up next week)

[patricklodder]

Closing this, like #2339, Qt 5.15 is unmaintained - we'd be wise to integrate 6.x if we can.