FW-177. Add cross-platform builds for simulation library.

* Supports x86-linux, amd64-windows, and x86-windows target build from an
  amd64-linux host, using MinGW-w64.
* Added two SCons build variables:
  * simhost   - simulation host architecture/OS to build
  * simhostpy - location of simulation host Python headers and library
* Added Scons tool module for MinGW-w64 support, and added SCons utils
  module.
* Reformatted SCons help text and provided more informative descriptions.