This commit skips a few more dist tragets during compilation which shouldn't be
necessary.
* First, when packaging std we only take action when the host target is the
build target. Otherwise we package the same artifacts a number of times, which
shouldn't be necessary.
* Next, we apply the same logic to the save-analysis build. This is actually
required for correctness as the build compiler is the only one which actually
has save analysis information. This should fix an error seen on nightlies.
Git worktrees have this as a file and typically won't work inside docker
containers, but that's ok, so instead of just checking for existence check for a
directory to see if the git commands will succeed.
This commit implements the `distcheck` target for rustbuild which is only ever
run on our nightly bots. This essentially just creates a tarball, un-tars it,
and then runs a full build, validating that the release tarballs do indeed have
everything they need to build Rust.
As the entry point for building the Rust compiler, a good user experience hinges
on this compiling quickly to get to the meat of the problem. To that end use
`#[cfg]`-specific dependencies to avoid building Windows crates on Unix and drop
the `regex` crate for now which was easily replacable with some string
searching.
The organization in rustbuild was a little odd at the moment where the `lib.rs`
was quite small but the binary `main.rs` was much larger. Unfortunately as well
there was a `build/` directory with the implementation of the build system, but
this directory was ignored by GitHub on the file-search prompt which was a
little annoying.
This commit reorganizes rustbuild slightly where all the library files (the
build system) is located directly inside of `src/bootstrap` and all the binaries
now live in `src/bootstrap/bin` (they're small). Hopefully this should allow
GitHub to index and allow navigating all the files while maintaining a
relatively similar layout to the other libraries in `src/`.
