Avio: fix FTBFS with lavf < 54
Missing #includes
os2: implement vlc_strerror() and vlc_strerror_c()

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
Revert "demux: ogg: don't recreate decoders on same chained streams."

This reverts commit 1f9c34275de478339dc4d750b8c62f1019303897.
demux: ogg: offset pcr on chained streams
demux: ogg: remove old debug info
demux: ogg: apply skeleton prior to es creation too
demux: ogg: clear initializing flag on oggds too
demux: ogg: fix es creation delaying with skeleton
demux: ogg: remove reset/delayed format updates.

No longer needed since ES are now created after headers.
demux: ogg: remove chained ogg boundary PTS handling

Shouldn't be needed anymore as we continue chain with offsetted PCR/PTS
demux: ogg: remove discontinuity flag

reused decoders won't need it.
demux: ogg: change pts/pcr generation from packets (fix #10198, fix #9605)

Stop using headers granule and invalid granule for PCR/PTS.
Delays until first PTS/PCR is really known. Avoids 0 to PTS gap
for non zero starting streams.
demux: ogg: reuse decoders when fmt is compatible (fix #5394)

Avoids rebuffering.
Wrong way reverted by 1d6f8d8174d4e2c704732f7ec13c71df6dd8950d
api: allow to change A/R on the fly.

ASF allows specifying a new aspect ratio while playing back.
Triggering change using the "aspect-ratio" variable can't work
for unknown A/R as the variable is "Checked" type.
demux: asf: follow aspect ratio payload extension (fix #7433)
demux: ogg: better track of es state
demux: ogg: don't create es for finished streams.

Should prevent presenting skeleton in es
libav: do not build avio and avformat on MERGE_FFMPEG (fixes #10251)
Qt: fix possible double-free on quit with simple volume widget