-Wunused-command-line-argument-hard-error-in-future is a harsh mistress
Apple updated the Xcode command line tools today, which upgraded clang to
Apple LLVM version 5.1 (clang-503.0.38) (based on LLVM 3.4svn) and enabled a feature in clang that causes unknown compiler flags to hard error rather than warn. The error is accompanied by an amusing/frustrating note:
clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
Apparently the future is here.
This is a serious problem because several common gcc flags are not supported under clang (most notably
For now you can work around the issue using
but be aware that this will stop working in a future clang.