Because I needed libvirt.

I have msys2/mingw64 but for my Golang cgo I have an alternative install

tdm-x86_64 + fedora mingw64 x86_64 packages

I used msys2 to hand compile pkg-config with these packages.

In this respect I have libvirt available to my golang.

It seems we have a libvirt PKGBUILD but no released package. Here is the MSYS2 approach to software development, shamelessly taken from ArchLinux. Could you try this:

    pacman -Ss base-devel mingw-w64-x86_64-toolchain
    git clone https://github.com/Alexpux/MINGW-packages.git
    cd MINGW-packages/mingw-w64-libvirt
    MINGW_INSTALLS=mingw64 makepkg-mingw -s
    pacman -U *pkg*xz

.. and if it doesn't work file a ticket on: https://github.com/Alexpux/MINGW-packages/issues

.. otherwise you should have an MSYS2 libvirt.

even if it does work, file a bug asking that mingw-w64-libvert gets packaged.

You really should not mix binaries from different ecosystems and compilers. I do not know how TDM configure their compilers or how Fedora configures theirs (exception models, C++ ABIs) but it is a risky business and I caution strongly against it. All your packages should be compiled with the same toolchain.

Why would you use TDM compilers anyway? MSYS2 comes with its own: pacman -S mingw-w64-x86_64-toolchain gets you the 64-bit version.

I keep the ecosystems tightly separated. I will try later today and inform you.