Auto merge of #1122 - gnzlbg:unused_macro, r=alexcrichton
Auto merge of #1122 - gnzlbg:unused_macro, r=alexcrichton

the f macro is unused in some targets

rust-lang/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc