bicon: unstable-2018-09-10 ->  unstable-2020-06-04
bicon: unstable-2018-09-10 ->  unstable-2020-06-04

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.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs