When shared libraries are unloaded, they are now removed from the target

ModuleList so they don't show up in the images. Breakpoint locations that are
in shared libraries that get unloaded will persist though so that if you
have plug-ins that load/unload and you have a breakpoint set on functions
in the plug-ins, the hit counts will persist between loads/unloads.

llvm-svn: 121069