bintools-wrapper: Don't stop set -u-ing

Same justification as previous commit.

pkgs/build-support/bintools-wrapper/default.nix

@@ -111,17 +111,13 @@ stdenv.mkDerivation {
 
   installPhase =
     ''
-      set -u
-
       mkdir -p $out/bin $out/nix-support
 
       wrap() {
         local dst="$1"
         local wrapper="$2"
         export prog="$3"
-        set +u
         substituteAll "$wrapper" "$out/bin/$dst"
-        set -u
         chmod +x "$out/bin/$dst"
       }
     ''
@@ -163,8 +159,6 @@ stdenv.mkDerivation {
         [[ -e "$underlying" ]] || continue
         wrap ${targetPrefix}$variant ${./ld-wrapper.sh} $underlying
       done
-
-      set +u
     '';
 
   emulation = let
@@ -307,7 +301,6 @@ stdenv.mkDerivation {
     ''
 
     + ''
-      set +u
       substituteAll ${./add-flags.sh} $out/nix-support/add-flags.sh
       substituteAll ${./add-hardening.sh} $out/nix-support/add-hardening.sh
       substituteAll ${../wrapper-common/utils.bash} $out/nix-support/utils.bash