Rollup of 3 pull requests

[frewsxcv]

• Successful merges: rustbuild: Fix recompilation of stage0 tools dir #41227, Updating docs for std::sync::Weak #29377 #41240, Fix invalid 128-bit division on 32-bit target (#41228) #41250
• Failed merges:

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (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 Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed.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.

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[frewsxcv]

@bors r+ p=10

[bors]

📌 Commit ad5c050 has been approved by frewsxcv

[bors]

⌛ Testing commit ad5c050 with merge 6aa0d9a...

[bors]

💔 Test failed - status-travis

[frewsxcv]

@bors retry

#40417

[bors]

⌛ Testing commit ad5c050 with merge b93a7d9...

[bors]

💔 Test failed - status-travis

[arielb1]

openssl build failed on x86_64-linux:

[00:51:17] error: failed to run custom build command for `openssl-sys v0.9.10`

[00:51:17] process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/release/build/openssl-sys-af1f288687ffbc04/build-script-build` (exit code: 101)

[00:51:17] --- stderr

[00:51:17] thread 'main' panicked at 'OpenSSL library directory does not exist: /checkout/obj/build/x86_64-unknown-linux-gnu/openssl/install/lib', /cargo/registry/src/github.com-1ecc6299db9ec823/openssl-sys-0.9.10/build.rs:55

[00:51:17] note: Run with `RUST_BACKTRACE=1` for a backtrace.

[alexcrichton]

That's likely #41227 at fault, I'll investigate