error when making documentation for libavl

[Shushundr]

I use Gentoo Linux with texinfo v7.1:

# emerge -pv =texinfo-7.1

...

 -*  sys-apps/texinfo
      Latest version available: 7.1
      Latest version installed: 7.1
      Size of files: 5 416 KiB
      Homepage:      https://www.gnu.org/software/texinfo/
      Description:   The GNU info program and utilities
      License:       GPL-3+

I am trying to compile the project with the following commands:
https://savannah.gnu.org/projects/avl with commands

$ git clone https://git.savannah.gnu.org/git/avl.git .
$ make docs
makeinfo --number-sections  libavl.texi
libavl.hdr:87: warning: environment command format as argument to @alias
libavl.texi:853: warning: @cindex should only appear at the beginning of a line
...

Files libavl.hdr and libavl.texi are generated with a texiweb program (from libavl repository), and, because of that, I can't change their content.