busybox: patchshebangs to fix build on "limited" /bin/sh builders

(cherry picked from commit b546c7440e)

pkgs/os-specific/linux/busybox/default.nix

@@ -43,6 +43,8 @@ stdenv.mkDerivation rec {
     ./busybox-in-store.patch
   ];
 
+  postPatch = "patchShebangs .";
+
   configurePhase = ''
     export KCONFIG_NOTIMESTAMP=1
     make ${if enableMinimal then "allnoconfig" else "defconfig"}