Merge cmake and autotools build steps for cygwin, msys2 and
cross-linux jobs.
Advantages:
- makes it easier to keep the two build tracks in sync.
- uses the same steps across jobs.
- avoids scrolling through greyed out steps.
- syncs steps with other workflows already merged like this.
- less code.
Also:
- stop ignoring WebSockets tests results for msys2/mingw-w64 cmake jobs,
except for 2301 2302 that were also ignored for autotools. Syncing the
two build methods.
- drop 'cmake' from step names where cmake was the only build tool.
This was redundant as "CM" already indicates it in the job name.
Closes#15643
2aa6d1a208