buildEnv: add new parameters: extraPrefix and buildInputs

pkgs/build-support/buildenv/builder.pl

···
 
 
 # Create the symlinks.
+my $extraPrefix = $ENV{"extraPrefix"};
 my $nrLinks = 0;
 foreach my $relName (sort keys %symlinks) {
     my ($target, $priority) = @{$symlinks{$relName}};
-    my $abs = "$out/$relName";
+    my $abs = "$out" . "$extraPrefix" . "/$relName";
     next unless isInPathsToLink $relName;
     if ($target eq "") {
         #print "creating directory $relName\n";

pkgs/build-support/buildenv/default.nix

···
   # directories in the list is not symlinked.
   pathsToLink ? ["/"]
 
-, # Shell command to run after building the symlink tree.
+, # Root the result in directory "$out${extraPrefix}", e.g. "/share".
+  extraPrefix ? ""
+
+, # Shell commands to run after building the symlink tree.
   postBuild ? ""
 
+, # Additional inputs. Handy e.g. if using makeWrapper in `postBuild`.
+  buildInputs ? []
+
 , passthru ? {}
 }:
 
 runCommand name
-  { inherit manifest ignoreCollisions passthru pathsToLink postBuild;
+  { inherit manifest ignoreCollisions passthru pathsToLink extraPrefix postBuild buildInputs;
     pkgs = builtins.toJSON (map (drv: {
       paths = [ drv ]; # FIXME: handle multiple outputs
       priority = drv.meta.priority or 5;