Help me test Visual C++ support

[KJK::Hyperion]

As of r41374, Visual C++ suppport in rbuild is almost fully functional
(PCH and full dependencies - i.e. rbuild -df - won't work yet. Also, the
Microsoft linker is not supported yet). All I need now is people working
to make sources compile with it. How to: add option -Mcmsc to variable
ROS_RBUILDFLAGS:

set ROS_RBUILDFLAGS=%ROS_RBUILDFLAGS% -Mcmsc

and build modules! make --keep-going will be very useful for the time
being. Now start fixing shit, for the love of god! go go go!