Create multi-arch nightlies

[brson]

Some people would like to be able to cross-compile from nightlies.

[alexcrichton]

Note that a script like this can be used to install a multi-arch nightly (by just downloading both)

target=unknown-linux-gnu
curl -O http://static.rust-lang.org/dist/rust-nightly-x86_64-$target.tar.gz
curl -O http://static.rust-lang.org/dist/rust-nightly-i686-$target.tar.gz
tar xf rust-nightly-x86_64-$target.tar.gz
tar xf rust-nightly-i686-$target.tar.gz
cp -r rust-nightly-i686-$target/lib/rustlib/i686-$target \
      rust-nightly-x86_64-$target/lib/rustlib
(cd rust-nightly-x86_64-$target && \
  find lib/rustlib/i686-$target/lib -type f >> lib/rustlib/manifest.in)
./rust-nightly-x86_64-$target/install.sh $@

[huonw]

This is happening as part of the new rustup/multirust, and there's probably a better/newer bug? (Maybe @brson, @alexcrichton or @edunham knows?)

At least #17356 is relevant.

[alexcrichton]

I also thought that there may be a newer bug but I can't seem to find it, so perhaps this can suffice!

[alexcrichton]

This is basically done with rustup now, so closing.