Re: Mingw task for Cirrus CI

I think the "only_if" should allow separately running one but not both of the
windows instances, like:

+  only_if: $CIRRUS_CHANGE_MESSAGE !=~ '.*\nci-os-only:.*' || $CIRRUS_CHANGE_MESSAGE =~ '.*\nci-os-only:[^\n]*mingw64'

I'm not sure, but maybe this task should only run "by request", and omit the
first condition:

+  only_if: $CIRRUS_CHANGE_MESSAGE =~ '.*\nci-os-only:[^\n]*mingw64'

I think it should include something like

+  setup_additional_packages_script: |
+    REM C:\msys64\usr\bin\pacman.exe -S --noconfirm ...

Let's see what others think about those.

Do you know if this handles logging of crash dumps ?

With tweaks to prep_buildtree, and with ./configure --cache-file, that step
goes down to ~36sec (unless configure needs to be re-run).

I also looked into using busybox to avoid running separate processes for each
"ln", but I think 36sec is good enough.

At one point, I tried setting "CIRRUS_SHELL: bash" to avoid writing "bash -c"
over and over, but never got it working.

-- 
Justin