[3.0] directx_va: fix detection of mingw-w64 v13 dxva.h
If the dxva.h file comes from the contribs, it doesn't match the system __MINGW64_VERSION_MAJOR. But we can detect it another way.
Similar to 20227126
If the dxva.h file comes from the contribs, it doesn't match the system __MINGW64_VERSION_MAJOR. But we can detect it another way.
Similar to 20227126
VideoLAN code repository instance