VS: Teach VS >= 10 generator about Windows CE

When CMAKE_SYSTEM_NAME is 'WindowsCE':

* Set the Subsystem and EntryPointSymbol accordingly.
* When CMAKE_SYSTEM_VERSION is 8.0 (Windows CE 2013),
  select the CE800 toolset by default.
Merge topic 'vs10-wince' into next

a3298f77 VS: Teach VS >= 10 generator about Windows CE