travis: Use upstream LLVM repositories for Fuchsia

[petrhosek]

The Fuchsia copies of LLVM repositories contain additional patches
for work-in-progress features and there is some amount of churn that
may break Rust. Use upstream LLVM repositories instead for building
the toolchain used by the Fuchsia builder.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aturon (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[petrhosek]

@alexcrichton could you please take a look? I hope the patch step is just the temporary solution until D28791 is resolved.

[alexcrichton]

@bors: r+

[bors]

📌 Commit b16101d has been approved by alexcrichton

[TimNN]

@bors r-

• Fails tidy (lines too long)

The best fix is probably to just mark the build-toolchain.sh file with # ignore-tidy-linelength.

[petrhosek]

Done.

[TimNN]

@bors r=alexcrichton

[bors]

📌 Commit b135c12 has been approved by alexcrichton

[bors]

⌛ Testing commit b135c12 with merge 53f4bc3...