`make install` doesn't work correctly with relative directory prefixes

[brson]

When I configured with --prefix=install-prefix and ran make install, my install ended up in ./tmp/empty_dir/install-prefix.

[0xmohit]

Seems to be because of cd here which was apparently added for #15558.

If the cd cannot be removed, then converting DESTDIR to absolute path before installing might work.

[Mark-Simulacrum]

I think this is still an issue with rustbuild, but should be somewhat easy to fix.. I think we just want to call canonicalize on the paths here: https://github.com/rust-lang/rust/blob/master/src/bootstrap/install.rs#L41. @alexcrichton Does that sound correct to you? If so, this is E-easy and E-mentor (by me).

[alexcrichton]

I believe so!

[toddboom]

@alexcrichton @Mark-Simulacrum I can take a crack at this one if nobody else has started on it yet.

[Mark-Simulacrum]

Go ahead! Let us know if there's anything we can do to help you.