I'm working on compiling webrtc under MinGW.
libwebrtc uses KSCATEGORY_VIDEO_CAMERA, which MinGW didn't have, but they added it to ksuser.c which gets compiled into ksuser.lib

However - we fail xul linking because ksuser.lib isn't linked and KSCATEGORY_VIDEO_CAMERA is not defined.
I don't know why this doesn't fail our normal windows builds; I suspect it's because ksuser gets implicitly linked somewhere. Or ksuser.c gets compiled into another dll we do link for Windows - but a grep of the Windows SDK only found it in ksuser.lib

Anyway, if I link ksuser into xul, I get duplicate symbol errors for KSDATAFORMAT_SUBTYPE_IEEE_FLOAT and KSDATAFORMAT_SUBTYPE_PCM.

These are defined in cubeb: https://searchfox.org/mozilla-central/rev/25997ce8267ec9e3ea4b727e0973bd9ef02bba79/media/libcubeb/src/cubeb_winmm.c#76-85

If I undefine them in cubeb then I get undefined symbol KSDATAFORMAT_SUBTYPE_IEEE_FLOAT, KSDATAFORMAT_SUBTYPE_PCM, and KSCATEGORY_VIDEO_CAMERA when linking xul. But then if I link ksuser into xul again, then everything works. So here's a patch that does that...

This fixes the MinGW compilation