Implements the various requirements for the runtime v2 code to abstract
away the unix/linux code into the appropriate platform level
abstractions to use the runtime v2 on Windows as well.
Adds support in the Makefile.windows to actually build the runtime v2
code for Windows by setting a shell environment BUILD_WINDOWS_V2=1
before calling make. (Note this disables the compilation of the Windows
runtime v1)
Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>
