They are defined since Linux 3.1 but not in musl yet.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

This PR fixes the build on all platforms and all Rust version down to the
minimum Rust version supported by libc: Rust 1.13.0.

The `build.rs` is extended with logic to detect the newer Rust features used by
`libc` since Rust 1.13.0:

* Rust 1.19.0: `untagged_unions`. APIs using untagged unions are gated on
  `cfg(libc_unions)` and not available on older Rust versions.

* Rust 1.25.0: `repr(align)`. Because `repr(align)` cannot be parsed by older
  Rust versions, all uses of `repr(align)` are split into `align.rs` and
  `no_align.rs` modules, which are gated on the `cfg(libc_align)` at the top
  level. These modules sometimes contain macros that are expanded at the top
  level to avoid privacy issues (`pub(crate)` is not available in older Rust
  versions). Closes #1242 .

* Rust : `const` `mem::size_of`. These uses are worked around with hardcoded
  constants on older Rust versions.

Also, `repr(packed)` structs cannot automatically `derive()` some traits like
`Debug`. These have been moved into `s_no_extra_traits!` and the lint of missing
`Debug` implementations on public items is silenced for these. We can manually
implement the `extra_traits` for these in a follow up PR. This is tracked
in #1243. Also, `extra_traits` does not enable `align` manually anymore.

Since `f64::to_bits` is not available in older Rust versions, its usage
has been replaced with a `transmute` to an `u64` which is what that method
does under the hood.

Closes #1232 .

Discovered while debugging: djg/audioipc-2#52

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).

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

Previous commit

dcff1547
"libc: changes to ppc64le musl branch to support building of rust on Alpine"

has removed stuff from mod.rs and added it to some submodules, but
missed the aarch64 submodule.

This copies the stuff that that commit added to the x86_64.rs submodule
and puts it into aarch64.rs.

amend to add style changes
amend to add style changes

These aren't exposed on non-MIPS musl targets, but since they're
part of a kernel API, they're still applicable, so we just don't
test them there but expose them anyways.

Note that termios2 doesn't exist on powerpc(64), termios
is used instead.

* Add syscall tables to most remaining arches in `src/unix/notbsd`
* Add aarch64/arm musl to CI
* Update dependencies

powerpc64 was missing in musl/mod.rs and making build fail
as it was not able to find types, like c_char.

Motivation: there is no glibc wrapper for this syscall

Signed-off-by: Tom Kirchner <tjk@amazon.com>
Signed-off-by: Ben Cressey <bcressey@amazon.com>

For some reason the type of ptrace request constants in musl change for the register based requests. As they are used in the same way and this doesn't mimic musl this has been changed for consistency and ease of use.

Rebase of #610 and also move emscripten up much higher in the hierarchy to
ensure that it doesn't have too much of a ripple effect on other platforms.

This involved moving down a good number of definitions, but hopefully was done
with care to not break anything!