Run export-validator on Windows

[MartinKavik]

Add export-validator Windows support.

Fixes #1231

Tested with just build on Windows 10 and Kubuntu 22.04 local machines.

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Note:
To make just build work on Windows I had to install Visual Studio with clang and then MinGW with ar and add both tools to PATH env var to make cross-compiler work.
On Linux, I had to install libfontconfig-dev and clang.

[hannobraun]

Thank you, @MartinKavik! Looks reasonable, and the CI build is green. Good to merge 👍

Note:
To make just build work on Windows I had to install Visual Studio with clang and then MinGW with ar and add both tools to PATH env var to make cross-compiler work.
On Linux, I had to install libfontconfig-dev and clang.

Something like this should probably go into CONTRIBUTING.md. I've made a note about that, and plan to take care it next week (either by doing that, or by opening an issue).