cc needs to know what stl was selected, promote stl from a generic
feature implementation to a fixed type pointer.
Change-Id: I950ef947f7cd254fe3074f4ff240bb2b90b9116c
Refactor all of cc in order to use composition instead of inheritance.
All cc module types exported by cc are now *cc.Module objects, with
compilation, linking, and installing steps delegated to different
objects in order to form the full module type. Additional features that
modify dependencies and flags can be inserted in a features object list,
and custom module types can be created by adding a Customizer object
that can modify properties.
Change-Id: Ie1283d14920f7856f6947b0530606b2f4d58fab0
