accept4 is not defined in libc for android

[elwerene]

In libc 0.2.87 there's no accept4 in unix/linux_like/android/mod.rs.
It is defined in unix/linux_like/linux/mod.rs, but this module is not loaded on android

[Thomasdezeeuw]

This is a regression in libc, not Mio. See rust-lang/libc#2101.

[Thomasdezeeuw]

For a quick fix add the following to your Cargo.toml:

[dependencies]
libc = "=0.2.86" # Note the `=` here.

[elwerene]

@Thomasdezeeuw I had to add libc as dependency to my project to fix the build as the dependency to libc without = is defined in https://github.com/tokio-rs/mio/blob/master/Cargo.toml#L49