Do not resolve symlinks when finding crates.

[taralx]

The resolved path may not end in '.rlib', causing us to try to read the
archive as an object file.

[rust-highfive]

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[taralx]

P.S. If there's a way to cherry-pick this into stable, that would be really nice.

[retep998]

If we're not going to use the result of canonicalize wouldn't it be better to just check whether the file exists? Also there's probably a good reason it uses canonicalize.

[taralx]

I went with a minimal change, but I can certainly switch to "file exists" if that's what's preferred. Canonicalize saves lookups later, but can result in a completely different filename.

In our case, the cloud builder creates symlinks of the form libcore-xyzzy.rlib -> /network/cas/$FILEHASH. Canonicalizing causes a "cannot find crate 'core'" error.

The alternative is to not rely on the filename past this point, making sure to pass down rlib-ness (and possibly more) as a parameter.

[eefriedman]

For reference, the behavior of resolving symlinks was added in #12474. I'm not sure if the original reason for adding that behavior is still relevant.

@alexcrichton might have something to say about it?

[taralx]

Apparently it does still matter. Okay, so I'll close this and rework it to not rely on the filename after canonicalization.