build(utils/dockerizedmake.pl): Helper tool to symlink a whole directory content.

utils/dirsymlink.pl

@@ -0,0 +1,19 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+my ($shadowdir, @keepdirs) = @ARGV;
+
+mkdir($shadowdir);
+
+system(qq#rm -f "$shadowdir"/*#);
+
+for my $k(@keepdirs) {
+  unlink("$shadowdir/$k");
+  mkdir("$shadowdir/$k");
+}
+
+system(qq#ln -rs .* * "$shadowdir"#);
+
+