Implment "platform process list" for Windows.

This patch implements basic functionality of the "platform process
list" command for Windows.  Currently this has the following
limitations.

* Certain types of filtering are not enabled (e.g. filtering by
  architecture with -a), although most filters work.
* The username of the process is not yet obtained.
* Using -v to list verbose information generates an error.
* The architecture column displays the entire triple, leading to
  misaligned formatting of the printed table.

Reviewed by: Greg Clayton
Differential Revision: http://reviews.llvm.org/D4413