Romain Vimont authored Apr 27, 2018 and Jean-Baptiste Kempf committed Apr 30, 2018

Do not declare *_sys_t typedefs globally in vlc_common.h. Instead,
declare them locally in each module that provides a definition.

This paves the way to move C++ definitions into anonymous namespaces in
order to respect C++ ODR.

The picture_resource_t and sout_stream_id_sys_t typedefs will be handled
separately, since they require specific additional changes.

See #18033

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