Remove unused variable. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187975 91177308-0d34-0410-b5e6-96231b3b80d8
Factor out parsing sanitizer arguments to a separate function

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187977 91177308-0d34-0410-b5e6-96231b3b80d8