stdenv: disable shellcheck rule SC2068 & SC1091

this is intentional to support both structuredAttrs and non

In pkgs/stdenv/generic/setup.sh line 614:
for pkg in ${depsBuildBuild[@]} ${depsBuildBuildPropagated[@]}; do
           ^------------------^ SC2068 (error): Double quote array expansions to avoid re-splitting elements.

In pkgs/stdenv/generic/setup.sh line 521:
    local varRef="$varVar[$((targetOffset - hostOffset))]"
                  ^-- SC1087 (error): Use braces when expanding arrays, e.g. ${array[idx]} (or ${var}[.. to quiet).

pkgs/stdenv/generic/setup.sh

@@ -1,5 +1,5 @@
 # shellcheck shell=bash
-# shellcheck disable=1090,2154,2123,2034,2178,2048
+# shellcheck disable=1090,2154,2123,2034,2178,2048,2068,1091
 __nixpkgs_setup_set_original=$-
 set -eu
 set -o pipefail