Add cputype recognition for Solaris

Fixes rust-lang#39729

Don't need to catch WindowsError.  That was very silly of me.

remove unnecessary gcc_s addition in libstd for Solaris

Add `swap` method for `Cell`

Addition to rust-lang#39264

r? @alexcrichton

…hton

Automate vendoring by invoking cargo-vendor when building src dist tarballs.

This avoids rust-lang#39633 bringing the `src/vendor` checked into git by rust-lang#37524, past 200,000 lines of code.

I believe the strategy of having rustbuild run `cargo vendor` during the `dist src` step is sound.

However, the only way to be sure `cargo-vendor` exists is to run `cargo install --force cargo-vendor`, which will recompile it every time (not passing `--force` means you can't tell between "already exists" and "build error"). ~~This is quite suboptimal and I'd like to somehow do it in each `Dockerfile` that would need it.~~

* [ ] Cache `CARGO_HOME` (i.e. `~/.cargo`) between CI runs
  * `bin/cargo-vendor` and the actual caches are the relevant bits
* [x] Do not build `cargo-vendor` all the time
  * ~~Maybe detect `~/.cargo/bin/cargo-vendor` already exists?~~
  * ~~Could also try to build it in a `Dockerfile` but do we have `cargo`/`rustc` there?~~
  * Final solution: check `cargo install --list` for a line starting with `cargo-vendor `

cc @rust-lang/tools

add solaris rustbuild support

Add Solaris as recognized ostype
Add cputype recognition for Solaris

Fixes rust-lang#39729

A future pull request will discriminate between the commercial release and older opensource derivatives to account for divergence, for now, this is compatible with both.

Fix some typos in the core::fmt docs.