Cargo Features

externc-libm has no features set by default.

[dependencies]
externc-libm = { version = "0.1.0", features = ["libm-unstable"] }
libm-unstable

Enables unstable of libm

libm:

This tells the compiler to assume that a Nightly toolchain is being used and that it should activate any useful Nightly things accordingly.

externc-libm has 1 feature without comment.