We now create an additional binary `linux_fcntl` for testing this
since there are header conflicts when including all necessary headers.
This binary is run on all platforms even though it's empty on all non-
Android/non-Linux platforms.

Testing has been switched from a custom binary to using a runner-less
test (or pair of tests). This means that for local development a simple
`cd libc-test && cargo test` will run all the tests. CI has also been
updated here to reflect that.

It's not supported on those platforms

*   correct sigaction
*   correct stat, alias stat64
*   remove doubled statvfs definition

OpenBSDs kqueue now has EV_RECEIPT and EV_DISPATCH.

I wrote a patch and the devs merged it into current:
https://marc.info/?l=openbsd-tech&m=149621427511219&w=2

This change extends the rust libc crate to provide the feature.

* Doesn't do much without getpwent/setpwent
* Not supported on Android before Android O

L4Re builds don't have default libraries. The L4Re build system controls
compilation and passes linker flags using -Z itself.

*   fix dirent, dirent64
*   port pthread_attr_t
*   add l4re-specific pthread code

64-bit Solaris/SPARC has a 4-byte pad before ai_addrlen for historical
reasons (ai_addrlen used to be defined as a size_t, which is 4 bytes in
ILP32 and 8 in LP64, but was converted to a 4-byte socklen_t in Solaris
10, which necessitated padding for (more or less) binary compatibility).

It has been added to glibc in version 2.26.

For some reason, they are in the NDK sources but
they are not available in the tests. I don't know what
Android does here, but nothing that makes sense.

I'd rather avoid the duplication, this is discussed in #707.