Make (most) tests build and run on Windows

I found myself on a Windows machine wanting to run tests, but could not, due to a number of issues. This MR attempts to address them as follows:

1. Builds cpp_test_static_library as static in Windows. Building as shared triggers the "export ordinal too large" issue that also plagues inkscape_base on MSYS2.
2. Disabled tests for libnrtype on Windows. There's an ifdef'd section that wants Inkscape::IO::Resource on Windows, but adding io/resource.cpp to the isolated list introduced in !7797 (merged) sets off a chain of dependencies that defeats the unit isolation. There's probably a better way to address this!
3. Fixes an ifdef'd typo in split-path-test.cpp
4. Adds some logic to the CLI test scripts to allow GraphicsMagick syntax, if ImageMagick can't be found.
5. Adds bc to the MSYS2 install list