Without the update build fails on -fno-common toolchains as:
$ nix build --impure --expr 'with import ./. {}; bicon.override { stdenv = clang13Stdenv; }'
...
ld: bicon_bin-bicon_read.o:/build/source/bicon/bicon_read.c:37:
multiple definition of `bicon_options'; bicon_bin-bicon.o:/build/source/bicon/./bicon_read.h:4: first defined here
While at it pulled in pending fix for clang compatibility.