Revert "patch-shebangs: use --build for auto patch shebangs"

Completely breaks darwin. Every package in the stdenv that has shebangs
in the output will end up with references to bootstrap-tools.

This reverts commit eb7c50a993.

pkgs/stdenv/generic/setup.sh

@@ -257,9 +257,17 @@ shopt -s nullglob
 
 # Set up the initial path.
 PATH=
+HOST_PATH=
 for i in $initialPath; do
     if [ "$i" = / ]; then i=; fi
     addToSearchPath PATH "$i/bin"
+
+    # For backward compatibility, we add initial path to HOST_PATH so
+    # it can be used in auto patch-shebangs. Unfortunately this will
+    # not work with cross compilation.
+    if [ -z "${strictDeps-}" ]; then
+        addToSearchPath HOST_PATH "$i/bin"
+    fi
 done
 
 if (( "${NIX_DEBUG:-0}" >= 1 )); then