CMake (MSVC): cmake automatically adds the /EHsc and /GR compiler

options. If we are building with exceptions/rtti disabled, we replace
/EHsc with /EHs-c- and /GR with /GR-, respectively. If we just add the
disabling options we get warnings like this:

cl : Command line warning D9025 : overriding '/EHs' with '/EHs-'

llvm-svn: 122648