Use 'unsigned' for enum bitfields
Use 'unsigned' for enum bitfields

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: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@299045 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang