Upstream: https://github.com/xiph/opus.git
Version:  1.6.1 (tag v1.6.1, commit 22244de5a79bd1d6d623c32e72bf1954b56235be)

Vendored by vendor.py in the parent directory; rerun it to update. It copies
the .c files the unity translation units compile and every header reachable
from them, and rewrites their includes as paths relative to the including
file.
