dxva2: disable vc1/wmv on Intel GPUs

The latest Intel drivers have started to expose the VC-1 decoder GUID, however
the decoder is still broken and crashes or produces a broken image.
Include wmcodecdsp.h and remove any duplicate GUID definitions
Support VC1/WMV3 Image codecs
Update opencore-amr libraries
Update Opus to 1.1rc2
Update libspeex to a recent build
Update build instructions for thirdparty libs
Update ffmpeg

Also re-enable --disable-doc, which was broken for a while.
Make sure side-data is merged until a proper solution is implemented
Disable the HQ Deint option on XP, to reduce user confusion
Update ffmpeg for matroska enhancements
Handle sample skips in the audio decoder

This is used by opus to drop pre-skip samples.
Fix timestamp resync after recent changes
Remove XP hint from tooltip, the option is now disabled there.
Update ffmpeg for DiscardPadding support
avcodec: use active_thread_type to check if mt decoding is active
Update ffmpeg
[MPC-HC] Use our own ffmpeg clone repository.

WARNING: This should be the first custom commit in our fork and its title should not be modified.
[MPC-HC] LAV Splitter: Exhibits MKV attachments through IDSMResourceBag interface.
[MPC-HC] Tray icon: Add an optional custom callback for "show property page" events.