This triggers a warning on a recent nightly, which in turn breaks CI due to
`#![deny(warnings)]` in libc-test/build.rs

This commit performs a number of updates for libc with the `wasm32-wasi`
target:

* Updates the `wasi-libc` repository commit used (previously known as
  `wasi-sysroot`)
* Updates the container to Ubuntu 19.10 which has Clang 9 packaged which
  is all we need.
* Avoids building `wasmtime` and instead downloads a precompiled binary.
* Updates bindings in `src/wasi.rs` to match the current upstream state.

sock_extended_err is a struct returned as a control message when the sockopt
IP_RECVERR is set, when recvmsg has the MSG_ERRQUEUE flag set.  IP_RECVERR and
MSG_ERRQUEUE are constants both already defined here.

This reverts commit 6ff2e8f1.

Signed-off-by: Yang Keao <keao.yang@yahoo.com>

Only Netlink interface link attributes up IFLA_STATS are currently
available. This commit adds IFLA_COST to IFLA_PROTO_DOWN.

See https://github.com/torvalds/linux/blob/54ecb8f7/include/uapi/linux/if_link.h#L106