[CI] Use ccache for Windows builds (#8332)

[CI] Use ccache for Windows builds (#8332)

On Ubuntu, there are ccache symlinks for `x86_64-w64-mingw32-gcc` and `x86_64-w64-mingw32-g++` but not the POSIX-specific variants. Furthermore, not all Linux distributions add the `-posix` suffix for that variant. Thus, this commit changes our Toolchain file to use the more generic `x86_64-w64-mingw32-gcc` and `x86_64-w64-mingw32-g++` compiler names and changes our CI to use the POSIX variant by default.