Replacing /GR with /GR- instead of applying both options to the project.  This should reduce some build bot warnings (D9025: "overriding '/GR' with '/GR-'").

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187836 91177308-0d34-0410-b5e6-96231b3b80d8