sbcl: Remove substution of 'gcc' with 'cc'
sbcl: Remove substution of 'gcc' with 'cc'

This substitution produces a nix-build warning, because the target
string was removed in commit 7b225df9a492977b8fff0948ce93c5ab31766f64
in 2016.

Remove the substition from the `postPatch` phase in `sbcl/common.nix`.

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