The aim of this is twofold: a) Clang warns when setting a deprecated
field in a definition and because several of the widely set
AVCodec fields are deprecated, one gets several hundred warnings
from Clang for an ordinary build. Yet fortunately Clang (unlike GCC)
allows to disable deprecation warnings inside a definition, so
that one can create simple macros to set these fields that also suppress
deprecation warnings for Clang. This has already been done in
fdff1b9cbf for AVCodec.channel_layouts.
b) Using macros will allow to easily migrate these fields to internal ones.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
