ccc: Support arguments which behave like linker inputs.

 - Support comma joined options which magically turn into multiple
   value arguments (e.g., -Wl,)

 - Split out separate Arg::render routine for when an argument is
   being rendered as an input (as opposed to in its original form).

 - Add option flag for options which should be rendered without the
   option when they are used as an input (e.g., -Xlinker or -o).

 - Support -weak-l..., -weak_framework, and -weak_library.

llvm-svn: 62075