Android's NDK typedefs __u64 as unsigned long long.

Linux 4.18 added support for SIGSYS info in signalfd. Add the new
fields to signalfd_siginfo.

While the kernel has support for these new fields now, no libc has
shipped a release with the new signalfd fields.

 - extattr_namespace_to_string()
 - extattr_string_to_namespace()

These are used by the flock wrapper in rustc_data_structures. The
constants were already present in x86_64-linux-gnu and BSD (since
4928bd98).

Also, alphabetize this section, since I'm merging two sections anyway.

Fixes #1113

DragonflyBSD does define 3 of these 14 functions.  But I elected not to
add it to the PR because I can't find any evidence that these syscalls
are used on Dragonfly, even in the base system.  And by themselves,
those three are insufficient for the xattr crate.

Also while here: fix powerpc64, mips, and mips64 pthread types.  These
targets are not yet fully/correctly implemented in rust-libc however.

Last commit fixed the function definition but not the constants.  Oops.

* Added ptrace and constants for all freebsdlike and netbsdlike OSs

Provide a symbol for the `ftok` function declared in sys/ipc.h, for completeness and to allow calling `ftok` to generate the key value for `shmat`.