libtools.make: add rule to build a DLL.

This only works for Windows, so you need to use it on Windows or set CROSS
accordingly.

Update mkamsboot to make mkamsboot.dll build and link against ucl.dll.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31333 a1c6a512-1295-4272-9138-f99709370657
2 files changed