Use C++ fields for C++ files

[cblp]

Fix

Warning: The following files listed in the main library's c-sources do not
have the expected '.c' extension
HsQML/dist-newstyle/build/aarch64-osx/ghc-9.6.7/hsqml-0.3.6.1/build/cbits/moc_Canvas.cpp,
HsQML/dist-newstyle/build/aarch64-osx/ghc-9.6.7/hsqml-0.3.6.1/build/cbits/moc_ClipboardHelper.cpp,
HsQML/dist-newstyle/build/aarch64-osx/ghc-9.6.7/hsqml-0.3.6.1/build/cbits/moc_Engine.cpp,
HsQML/dist-newstyle/build/aarch64-osx/ghc-9.6.7/hsqml-0.3.6.1/build/cbits/moc_HighDpiScaling.cpp,
HsQML/dist-newstyle/build/aarch64-osx/ghc-9.6.7/hsqml-0.3.6.1/build/cbits/moc_Manager.cpp,
HsQML/dist-newstyle/build/aarch64-osx/ghc-9.6.7/hsqml-0.3.6.1/build/cbits/moc_Model.cpp.
C++ files should be in the 'cxx-sources' stanza.
See
https://cabal.readthedocs.io/en/3.10/cabal-package.html#pkg-field-cxx-sources

[cblp]

I don't know what's wrong with appveyor. It's better to re-check after fixing C++ warnings #20

[prolic]

I don't know what's wrong with appveyor. It's better to re-check after fixing C++ warnings #20

It seems like linking is broken on Windows builds. Maybe it's because of this?

HsQML/Setup.hs

Line 199 in ded7e5c

(map ((bDir </>) . flip replaceExtension objExtension) $ cSources bi))