Updated detection of cross-compilation support

Updated detection of cross-compilation support
Added a script for x-compiling necessary libraries
    initialize_project.sh
    utils/scripts/crosscompile_libs.sh   (+)
Added wind64 cross-compilation setup and fixes

Added wind64 cross-compilation setup and fixes

Windows target is now build under build/win
Linux target is built under build/linux

Various fixes of what win64 x-compile didn't like.
Separated target difference to utils/win_build.py and
utils/linux_build.py.

The empty file utils/__init__.py just makes it so
we can use "import from utils win_build as c"

I've also added a SCons help utility by the
SCons foundation, that I modified a bit.
This makes x-compilation easier.
Tis file is utils/scripts/crossmingw.py

    SConstruct
    external/flite/SConscript
    external/flite/src/SConscript
    external/noise/SConscript
    external/noise/src/SConscript
    external/polyvox/SConscript
    external/polyvox/library/PolyVoxCore/SConscript
    external/polyvox/library/PolyVoxUtil/SConscript
    src/SConscript
    src/SConscript_tests
    src/core/MainManager.cpp
    src/graphics/GlCheck.cpp
    src/graphics/GlCheck.h
    src/graphics/GraphicsManager.cpp
    src/graphics/GraphicsManager.h
    src/graphics/Mesh.cpp
    src/graphics/SDL_opengl.h
    src/util/LogUtil.cpp
    src/util/TestException.h
    src/util/TextBoxText.cpp
    src/util/TimedExecution.cpp
    src/util/TimedExecution.h
    utils/__init__.py           (+)
    common_build.py -> utils/linux_build.py
    utils/scripts/crossmingw.py (+)
    utils/win_build.py          (+)
Updated README.md to mention win64 x-comp

Updated README.md to mention win64 x-comp
    README.md