dfcfaa4ec1
LLVM really dislikes this and will assert, saying something along the lines of: ``` rustc: llvm/lib/MC/MCSubtargetInfo.cpp:60: void ApplyFeatureFlag( llvm::FeatureBitset&, llvm::StringRef, llvm::ArrayRef<llvm::SubtargetFeatureKV> ): Assertion `SubtargetFeatures::hasFlag(Feature) && "Feature flags should start with '+' or '-'"` failed. ```