CI: compile OSGeo4W-Windows build with clang

[nilason]

The last week the Windows CI runner failed with linking failure, the reason was reported here: msys2/MINGW-packages#15469. Searching for a fix/alternative/solution I came up with this PR.

The original solution has now apparently been fixed, but I put this up as a "proof of concept".

[hellik]

I put this up as a "proof of concept".

for some kind of a "general" switch to clang?

[nilason]

I put this up as a "proof of concept".

for some kind of a "general" switch to clang?

Would that really be such a bad thing?

Anyways, I had no intention to actually pushing for this PR, but put it up in case a similar situation comes up with no working CI runner for Windows.
(On the other hand MS and Visual Studio seems to embrace clang in general, soo....)
All the same, I'll leave this PR on the shelf (just like #2281), to reach for if needed.

[hellik]

Would that really be such a bad thing?

not a bad thing :-)

Just a case of curiosity

[nilason]

Would that really be such a bad thing?

not a bad thing :-)

Just a case of curiosity

I think the CI runner should reflect the way the release build is built. Now, the release dist is built with gcc, then gcc should preferably be used for CI too. But if the CI not working for a prolonged period of time, it's good to have an alternative.

[echoix]

Is it worth keeping the draft open, or simply closing it unmerged and reference it when needed (or reopening) if ever it is needed?