Log message:
libplacebo: update to 6.338.2.

v6.338.2

This release fixes a number of minor issues with v6.338.1, in particular
a fix for the new caching subsystem when using custom cache callbacks.

Fixes and performance improvements:
- properly align AVFrame planes when using oddly-sized pixels
- correct some reported GPU buffer size limits
- properly report texture transfer failures
- avoid ICC-related error spam
- avoid using some deprecated APIs and syntax
- fix pl_find_filter_* missing symbols
- fix duplicate initialization of vulkan debug layers
- fix assertion when using custom cache allocator API
- avoid redundant scale shader variable declarations
- avoid redundant linearization step when using sigmoid scaling
- avoid generating redundant dependency on xxhash
- fix possible integer overflow on 32-bit textures
- fix cropped frame dimensions when using vulkan hwframes

Log message:
libplacebo: Avoid use of illegal reserved typedef, helps build on SunOS

Log message:
libplacebo: actually requires C++20

Log message:
libplacebo: Import libplacebo-6.338.1 as multimedia/libplacebo

libplacebo is, in a nutshell, the core rendering algorithms and ideas
of mpv rewritten as an independent library. As of today, libplacebo
contains a large assortment of video processing shaders, focusing on
both quality and performance.

Packaged in pkgsrc-wip by <leot> and <wiz>.

This will be needed for multimedia/mpv.