FFmpeg Windows 8.1 build broken for submodule version after origin/master

[dananarama]

Following the WinRT build instructions, the Windows 8.1 build fails for commits after the current origin/master (69fd3e2). When building with the next commit that changes the submodule (3ed7129), the Windows 8.1 build breaks with the following messages:

hwcontext_d3d11va.o : error LNK2019: unresolved external symbol CreateMutex referenced in function d3d11va_device_init
libavutil/avutil-55.dll : fatal error LNK1120: 1 unresolved externals
make: *** [/c/records/projects/ffmpeginterop/FFmpegInterop/ffmpeg/ffbuild/library.mak:102: libavutil/avutil-55.dll] Error 96

I realize that this is an FFmpeg issue and not FFmpegInterop, but was unsure whether it was the WinRT build instructions that needed to be updated. Let me know if I should post this somewhere else.

Thanks.