- some tests are failing
- remove readlink, timegm and sig* functions in favor of the
  unix/mod.rs definitions
- remove time64_t (it is not defined for aarch64)
- move some definitions to android/b32.rs and create appropriated
  definitions in android/b64.rs

Apparently a lot of libc's don't put "const" on the return type for
readdir, which causes type mismatch.

The readdir_r call has problems, and we'll probably want to move to
readdir on many, if not most, unix targets. This patch makes readdir
available in unix, rather than just solaris as before.

See https://github.com/rust-lang/rust/issues/40021

For compatibility reasons, Solaris historically had its header files
setup so that, unless specifically requested through specific header
defines, either the old pre-POSIX interfaces or POSIX.1c Draft 6
interfaces were used. However, in the case of rust, since these symbols
are linked directly instead of via system header files, the underlying
posix symbol name can be used directly instead.

These definitions should be corrected to match what they do on almost
every other platform.

Be aware this is a breaking change in terms of interface for any crates
/ consumers of these interfaces for Solaris.

Fixes #522

Fixes #517

* pthread_t is defined as uint_t, so must be c_uint, not uintptr_t, just
  as pthread_key_t is already defined
* fd_set is defined as long, so must be i32/i64 based on
  target_pointer_width; this also fixes an indirect endianness issue
  encountered on sparc
* FD_SETSIZE should be defined as 65536 when target_pointer_width = 64

Fixes #515

`aarch64.rs` was copied and adapted from `x86_64.rs`.

The wcstombs() function conforms to ISO/IEC 9899:1999 (``ISO C99'')

https://github.com/rust-lang/libc/pull/501

It turns out that *only* FreeBSD and NetBSD proper have waitid, and that
Solaris' additional W* constants are totally different from everyone
else's, which tips me over from 'find some way to shoehorn this into
the top-level unix/mod.rs' to 'put it in the submodules, live with the
code duplication'.

 * OpenBSD doesn't have idtype_t or the P_* constants either
 * FreeBSD has different values for the P_* constants
 * Android gives idtype_t a different signedness
 * Disable waitid on NetBSD as it causes a link failure - I think this
   may be a problem with the test environment

This is a wrapper around getsockopt() for getting the uid/gid of a
remote Unix domain socket peer. It was added in FreeBSD 4.6 and present
in all modern BSDs I checked (including Mac OS X).

 * idtype_t no longer an enum.
 * Darwin/x86-32 needs the $UNIX2003 thing.
 * Darwin, FreeBSD, and NetBSD all have different values for the new constants.
 * OpenBSD doesn't have this feature at all.  (Hopefully we can get away
   with defining idtype_t anyway.)

waitid() is a variation on waitpid() with a marginally more
convenient way of reporting the status, and a couple of handy
additional features, such as the ability to peek at an exit
status without consuming it.  It's in POSIX.1-2008 and should
be available on all supported Unixes.

Along with it come the type 'idtype_t' and the constants
WEXITED, WSTOPPED, WCONTINUED, and WNOWAIT.  Theconstants
were alre dy defined for unix/notbsd platforms.

Patch incomplete: several targets are going to have to add
definitions of siginfo_t, but I'm not sure which ones yet.

Solaris doesn't implement flock(), so any Rust implementation of flock()
will need to implement it using fcntl(), using the F_RDLCK, F_WRLCK, and
F_UNLCK constants.