Incorrect .dll file names

[Lootwig]

The sample .dart files reference "xyz_library/Debug/[sample name].dll", whereas the created files are "xyz_library/lib[sample_name].dll".

[dcharkes]

cc @domesticmouse

[domesticmouse]

I haven't had enough time to dig into figuring out why CMake does what it does. Perchance is there a CMake person on the team?

/cc @cbracken