- under openbsd/bitrig it is 256
- change type to `size_t` where system have `getnameinfo()` with
  `hostlen` as `size_t`

under openbsd it is a `caddr_t` which expand to `char *`.
as the size of the type change, adjust the padding too.

- openbsd
- bitrig
- netbsd

arguments `hostlen' and `servlen' are `socklen_t' or `size_t' depending
the platform

- apple: I don't known, so I don't change the original definition (socklen_t)
- netbsd: socklen_t
- freebsd: size_t
- dragonfly: size_t
- openbsd: size_t
- bitrig: size_t

- sysctl: *mut -> *const
- mprotect: *const -> *mut
- remove sysctlbyname() that don't exists under openbsd

- same prototype on bitrig and openbsd
- for netbsd, I did found it at all (?)

- IPV6_{ADD,DROP}_MEMBERSHIP
- HW_AVAILCPU

- under openbsd and bitrig: dli_saddr member is *mut ::c_void
- under netbsd: it is *const ::c_void

Add emscripten support

openbsd: map `si_addr` inside `struct siginfo_t`

formally, under OpenBSD, `si_addr` is part of a C union. As we don't use
others members of the union inside `struct siginfo_t`, it should be safe
to directly map the field.

Update the android CI image

It's got a new toolchain which should hopefully support some more modern
definitions.

Add getentropy(2)'s syscall number as a const

I'm not convinced that the NR_* naming scheme is ideal, but it's pretty
good.

I didn't recognize any other syscall numbers in the file, so I started a
new section.

Bump to 0.2.4

Fix compiles on various BSDs

Also document them to prevent future regressions

Add binding for memrchr on Linux

Bump to 0.2.3

Add a load of constants/definitions from nix

This is a blanket import of lots of constants and function from nix-rust

Expose functionality to get peer credentials for a Unix socket on Linux

Add PATH_MAX for FreeBSDlike, defined in /usr/src/sys/sys/syslimits.h