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

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-'

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122648 91177308-0d34-0410-b5e6-96231b3b80d8