This fixes "%m" in error dialogs on non-GNU platforms.

Those are more flexible than the GNU-specific %m format specifier to
print standard error messages. They are also less likely to format a
clobbered error number.

With the introduction of CODEC_FLAG_OUTPUT_CORRUPT incomplete frames
are silently dropped. Enable it to maintain the previous behaviour.

Close #10140
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Close #8691

Of course, because we _really_ need that many RGB formats...

From 51.49.100 to 51.74.100, it only defines PIX_FMT_YUVA422P and not
AV_PIX_FMT_YUVA422P. There are other ways to fix, but ugly. And people should
update their FFmpeg anyway :)