VS: Fix handling of non-preprocessor flags in CMAKE_RC_FLAGS

Teach the VS >= 10 generator to honor flags other than -I and -D
in the CMAKE_RC_FLAGS[_<CONFIG>] variable.  Place them within the
ResourceCompile .vcxproj element under AdditionalOptions.

Also add a rudimentary flag map to map '-n' to 'NullTerminateStrings'.
Merge topic 'vs-RC-flags' into next

5d873846 VS: Fix handling of non-preprocessor flags in CMAKE_RC_FLAGS