Fixes this clang warning on Windows:

warning: implicit truncation from 'clang::LangOptions::FPContractModeKind' to bit-field changes value from 2 to -2 [-Wbitfield-constant-conversion]
    fp_contract = LangOptions::FPC_Fast;
                ^ ~~~~~~~~~~~~~~~~~~~~~



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@299045 91177308-0d34-0410-b5e6-96231b3b80d8