MSVC: Add "use File::Path qw(rmtree)".

My back-patch of commit 10b72dea added
calls to File::Path::rmtree(), but v10 and older had not been importing
that symbol.  Back-patch to v10, 9.6 and 9.5.

src/tools/msvc/vcregress.pl

@@ -10,6 +10,7 @@ use Cwd;
 use File::Basename;
 use File::Copy;
 use File::Find ();
+use File::Path qw(rmtree);
 use File::Spec;
 BEGIN  { use lib File::Spec->rel2abs(dirname(__FILE__)); }