Improved Support for Clang and new Qt Version: 5.15 (on Mac)

[jonoomph]

Adding Qt 5.15 support for Mac builds, and misc fixes to allow clang++ and clang to correctly build libopenshot. This bumps the minimum Mac OS X version to 10.13 (due to our pre-compiled Qt library). In the future, we can compile that ourselves, and drop the minimum back to 10.9 (if there is a demand for it).

Also, changes GitLab builder to new Linux builder,

Related to PRs:
OpenShot/libopenshot-audio#100
OpenShot/openshot-qt#3604

[codecov]

Codecov Report

Merging #549 into develop will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##           develop     #549   +/-   ##
========================================
  Coverage    48.77%   48.77%           
========================================
  Files          129      129           
  Lines        10036    10036           
========================================
  Hits          4895     4895           
  Misses        5141     5141           

Impacted Files	Coverage Δ
include/ChunkReader.h	0.00% <ø> (ø)
include/ChunkWriter.h	0.00% <ø> (ø)
include/FrameMapper.h	75.00% <ø> (ø)
include/KeyFrame.h	100.00% <ø> (ø)
include/Profiles.h	0.00% <ø> (ø)
include/ReaderBase.h	100.00% <ø> (ø)
include/Settings.h	50.00% <ø> (ø)
include/ZmqLogger.h	33.33% <ø> (ø)
src/Frame.cpp	47.70% <0.00%> (ø)
src/Qt/PlayerDemo.cpp	0.00% <ø> (ø)
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6638f41...6b94dbb. Read the comment docs.

[jonoomph]

I'm not sure I understand the codecov/patch failure...

[ferdnyc]

@jonoomph The explanation is shown in the detail view, though it still takes a bit of unpacking. Specifically, at this point in the diff:
https://github.com/OpenShot/libopenshot/pull/549/files#diff-76f89b751d681404c52704a8e267f8f0

Codecov flags an "added" (really edited, but they count it as added) line of code as not being covered by tests. That line is the only line of program source in the entire PR (all the rest are #includes or other non-program-code lines).

One of Codecov's criteria is what percentage of the diff adds lines that have unit test coverage. I think the default settings expect at least 50% coverage for code in the diff. (Obviously with only one qualifying line, the only real possibilities are 100% or 0%.)