Implement multiple output support (e.g. .dll linking)

[bird]

When linking a DLL on windows there is one or two extra files being generated that's of importance, esp. the import library. These are currently copied to PATH_LIB without really telling anyone and thereby screwing up dependencies. It should be made possible to suppress this copying, control where it copies the files, and there must of course be the correct rules and such so make can figure the right order in which to link stuff.

[bird]

We're telling kmk about the extra output so it'll do the right thing, so the worst part is fixed here.