[CI] Add llvm-mingw

[past-due]

Add llvm-mingw CI pass.

Depends on:

• mingw compilation fixes crashpad#78
• Fixes for mingw builds (+ ARM64) #794

[codecov]

Codecov Report

Merging #797 (299a50a) into master (596260c) will decrease coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #797      +/-   ##
==========================================
- Coverage   81.21%   81.18%   -0.03%     
==========================================
  Files          53       53              
  Lines        6947     6947              
  Branches     1112     1112              
==========================================
- Hits         5642     5640       -2     
- Misses       1195     1196       +1     
- Partials      110      111       +1     

[supervacuus]

Thank you for this contribution @past-due!

Please let me also be clear about what this CI addition means in terms of maintenance responsibility:

• the responsibility to fix issues concerning MinGW crashpad support still lies with the community
• if the build fails, we will create an issue tagging whoever is interested (I would certainly tag you @past-due)
• if no one is found who has the time to fix the issue, we will deactivate the build so as not to block progress on topics orthogonal to MinGW
• if no one fixed the issue until the next release, the changelog will contain a note that the MinGW support for crashpad is broken (referencing the tracking issue)

@Swatinem, let us finish the remaining crashpad updates in a separate PR and remove the submodule update here.

[supervacuus]

CC: @bitsandfoxes @markushi

[past-due]

Please let me also be clear about what this CI addition means in terms of maintenance responsibility:

• the responsibility to fix issues concerning MinGW crashpad support still lies with the community
• if the build fails, we will create an issue tagging whoever is interested (I would certainly tag you @past-due)
• if no one is found who has the time to fix the issue, we will deactivate the build so as not to block progress on topics orthogonal to MinGW
• if no one fixed the issue until the next release, the changelog will contain a note that the MinGW support for crashpad is broken (referencing the tracking issue)

Sounds great. 👍

Please feel free to tag me if / when any future breakages happen.