The vendor-defined XTHeadBb (predating the standard Zbb extension)
extension adds some bit-manipulation extensions with somewhat similar
semantics as some of the Zbb instructions.
It is supported by the C9xx cores (e.g., found in the wild in the
Allwinner D1) by Alibaba T-Head.
The current (as of this commit) public documentation for XTHeadBb is
Support for these instructions has already landed in GNU Binutils:
Depends on D143036