Use the suggestion from http://support.microsoft.com/kb/2262855 to escape
semicolons in preprocessor definitions for VS >= 10. Update the
COMPILE_DEFINITIONS documentation disclaimer list of known limitations
accordingly. Update our "Preprocess" test to cover the case.
Suggested-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>
Some values simply cannot be escaped properly in all contexts for all
native build tools. Document known limitations after the disclaimer
that states so.