Support building with MSVC

[ishitatsuyuki]

This is a series to support building dxvk-nvapi on MSVC for fun, diversity and binary size reduction. In addition to MSVC, cross compiling from Linux with clang-cl is also supported using https://github.com/mstorsjo/msvc-wine and a cross file like https://gist.github.com/ishitatsuyuki/bfa4b4764394f94b19115b182d269f4e.

Most changes are described in the commit message. This is a list of major breaking changes for those who need to rebase:

• When declaring a new extension interface, declare the GUID in the header using __CRT_UUID_DECL instead of FOO_GUID. The .cpp files are deleted and the guid field no longer needs to be assigned manually.
• When writing tests, use __uuidof instead of ::guid or IID_.
• When introducing new D3D12 mocks, methods than return a struct by value will need different mocks for MinGW and MSVC. See tests: Make mocks compatible with MSVC COM return ABI for an example.

[ishitatsuyuki]

Actually, forgot one change to add dllexport to nvapi_queryinterface. One sec.

[ishitatsuyuki]

Thanks for the quick review!