Linux/VAAPI: implement vaSyncBuffer stub for libva <2.9.0

[psyke83]

Description

Implement vaSyncBuffer() stub for libva <2.9.0, which allows Ubuntu 20.04 builds of Sunshine to be linked against ffmpeg built against libva 2.9.0 or later.

The vaSyncBuffer() function is needed for the async_depth VAAPI encoder parameter to work correctly, which can reduce latency if GPU drivers support the interface.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated