Update GHA Ubuntu version to 20.04

Add more TCP options for solaris systems.

This adds the `TCP_KEEPCNT` and `TCP_KEEPINTVL` tcp values to the libc crate. It also corrects the value of `TCP_KEEPIDLE` for Solaris systems. As seen in the diff, the value is different between illumos and Solaris (as the feature was added after the two code bases forked, and each ended up choosing a different value).

Adding these to libc will allow the nix crate to utilize them when used on solarish systems.

Update redox socket constants

Add endservent, getservbyport, getservent, setservent

Rollup of 2 pull requests

Successful merges:

 - #1953 (Add dl_iterate_phdr to some BSD OSs)
 - #1960 (Disable `sparc-unknown-linux-gnu` for now)

Failed merges:

r? `@ghost`

Disable `sparc-unknown-linux-gnu` for now

Add dl_iterate_phdr to some BSD OSs

Add dl_iterate_phdr for freebsd, openbsd and netbsd: #1066
cc https://github.com/rust-lang/backtrace-rs/issues/325

* Include some header files
* Ingore tests for p_type field of `Elf*_Phdr` because of
  conflicting with p_type macro from resolve.h

Release 0.2.80

Allow `deprecated` attribute on `f!` macros to fix dragonfly build

Fixes #1957
cc `@nagisa` I think this should resolve the build :)

Add a deprecation note to `time_t` on musl

cc #1848

Revive tests for MIPS64

This reverts commit 6e719f77.

This reverts commit 7aa60269.

linux: Add definitions for Multipath TCP

The Linux kernel recently gained support for [Multipath TCP](https://en.wikipedia.org/wiki/Multipath_TCP), a protocol which builds upon TCP. This patch adds `IPPROTO_MPTCP` to open new sockets and `TCP_ULP` to query the upper layer protocol of traditional TCP sockets (which is set to `mptcp` for all underlying connections)

Source: [tcp: Define IPPROTO_MPTCP](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=faf391c3826cd29feae02078ca2022d2f912f7cc)

cc #1896

Co-authored-by: Yuki Okushi <huyuumi.dev@gmail.com>

Bring the MUSL version of siginfo_t up-to-date.

**Background**

As far as I can tell, the [current MUSL version of `siginfo_t`](https://git.musl-libc.org/cgit/musl/tree/include/signal.h#n97) includes fields like [`si_pid`](https://git.musl-libc.org/cgit/musl/tree/include/signal.h#n108) and [`si_uid`](https://git.musl-libc.org/cgit/musl/tree/include/signal.h#n109).

**Change**

This update unifies `siginfo_t` support between GNU and MUSL.

Unpin the `cc` crate version

Fixes #1933

Add constants of socket options

Signed-off-by: Kenta Tada <Kenta.Tada@sony.com>

Signed-off-by: Kenta Tada <Kenta.Tada@sony.com>