configure: Suppress "potentially uninitialized variable" warnings from MSVC

The same is done for GCC and clang already.
rv34: use ff_mpeg_update_thread_context only when decoder is fully initialized

MpegEncContext based decoders are only fully initialized after the first
ff_thread_get_buffer() call. The RV30/40 decoders may fail before a frame
buffer was requested. ff_mpeg_update_thread_context() fails on half
initialized MpegEncContexts. Since this can only happen before a the
first frame was decoded there is no need to call
ff_mpeg_update_thread_context().

Based on patches by John Stebbins and tested by John Stebbins.

CC: libav-stable@libav.org
electronicarts: do not fail on zero-sized chunks

At least one FATE sample contains such chunks and happens to work simply
by accident (due to find_stream_info() swallowing the error).

CC: libav-stable@libav.org
electronicarts: read the framerate for MAD
electronicarts: set the framerate for TGQ/TQI

It is hardcoded to 15fps.
ogg: Provide aliases for Speex, Opus and audio-only ogg

Since they are aliases for ogg enabling any of them enables ogg as well.
os_support: Undefine lseek/stat/fstat before defining them

This avoids a number of redefinition warnings on MinGW64.
qt-faststart: Undefine fseeko/ftello before defining them

This avoids a number of redefinition warnings on MinGW64.
Merge commit 'b0bfd09f88da8b7c7666faf0ac7d5e74559dba9f'

* commit 'b0bfd09f88da8b7c7666faf0ac7d5e74559dba9f':
  configure: Suppress "potentially uninitialized variable" warnings from MSVC

Conflicts:
	configure

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'dc4b2e7d33903a6b9380e8a84b22b3a20facbb08'

* commit 'dc4b2e7d33903a6b9380e8a84b22b3a20facbb08':
  rv34: use ff_mpeg_update_thread_context only when decoder is fully initialized

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '4d6c5152849e23a4cc0f6a6ac2880c01ebcd301b'

* commit '4d6c5152849e23a4cc0f6a6ac2880c01ebcd301b':
  electronicarts: do not fail on zero-sized chunks

Conflicts:
	libavformat/electronicarts.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
wavpack: check number of channels

This means container and codec disagree. The codec is supposed to
know better so this could be an error instead.
wavpackenc: reset trailer info on block encoding

In some cases, in particular if several blocks are needed because of
the channel layout (e.g. 2.1), the information used to write the
trailing bits terminating the sample data was not reset.

This would cause potential desync on the decoder, although decoded
samples were actually mostly fine.

Fixes ticket #3879.
Merge commit '7b6aae23e12f41cdfac7f1069debfe44d9a3d136'

* commit '7b6aae23e12f41cdfac7f1069debfe44d9a3d136':
  electronicarts: read the framerate for MAD

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'cb7b1a2dfb547ab78342a7a9d5cd729d77d90421'

* commit 'cb7b1a2dfb547ab78342a7a9d5cd729d77d90421':
  electronicarts: set the framerate for TGQ/TQI

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '051aadeed104ecbe8ee4850ec2d7e5394f5e1ccd'

* commit '051aadeed104ecbe8ee4850ec2d7e5394f5e1ccd':
  ogg: Provide aliases for Speex, Opus and audio-only ogg

Conflicts:
	Changelog
	libavformat/oggenc.c
	libavformat/version.h

See: 2ccc6ff03acc3ca31db1aeb828c747d05b5cb6aa
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '1019b7c4edff537499c4a6cb0d65abae04ce58f6'

* commit '1019b7c4edff537499c4a6cb0d65abae04ce58f6':
  os_support: Undefine lseek/stat/fstat before defining them

Conflicts:
	libavformat/os_support.h

See: ef122ff5072463366c020157f0a27aad7e6610db
See: ed3c0fe85dd5c228e98126b18e50ffb617e77070
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '3526ab891c28396ada8b58bf7647309bab30de1d'

* commit '3526ab891c28396ada8b58bf7647309bab30de1d':
  qt-faststart: Undefine fseeko/ftello before defining them

Merged-by: Michael Niedermayer <michaelni@gmx.at>
vidstab*: Remove accidentally exported av_2_vs_pixel_format()

Also correctly namespace other functions in vidstabutils, and decrease
difference from Libav.

Initial-patch-by: Vittorio Giovara <vittorio.giovara@gmail.com>
Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vidstabutils: improve documentation

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>