Clang, cmake & make issues when trying to build on windows

I tried to force testing on windows however I have funny problems with clang being in wrong path or incorrect (i wanted to use mingw one). cmake check says:

-- Check for working CXX compiler: C:/Program Files/LLVM/bin/clang++.exe
-- Check for working CXX compiler: C:/Program Files/LLVM/bin/clang++.exe - broken

however I wanted build to use clang from:

mingw-w64-x86_64-clang /mingw64/bin/clang++.exe
mingw-w64-x86_64-clang /mingw64/bin/clang.exe

The build in question is in https://travis-ci.org/github/darktable-org/darktable/jobs/736897069

we have windows build instructions that do work, but for some reason I can’t replicate build on travis’ windows: https://github.com/darktable-org/darktable/blob/master/packaging/windows/BUILD.txt

Try using the $mingw64 prefix instead of the $msys2 prefix when calling "$SRC_DIR/.ci/ci-script.sh". That should place /mingw64/bin in the PATH, and is equivalent to opening a MINGW64 window in your instructions.