On, windows, don't delete a static library if it does not exists.

The "del" command does not have a switch to prevent warning if file
does not exists, so need extra shell magic.


[SVN r31034]

tools/build

@@ -1 +1 @@
-Subproject commit ec673c840f44db4e4d1a45a2ea84f973c7c726e7
+Subproject commit 665d0b55ddf2319f4653c7142c0c474df5ae9530