-Z build-std stopped working in 7/29 rust nightly

[jdm]

surfman's CI has the following using the nightly rustc compiler:

cd surfman
rustup component add rust-src --target=aarch64-uwp-windows-msvc
cargo build -Z build-std --verbose --target=aarch64-uwp-windows-msvc

This regressed on 7/29, according to https://travis-ci.com/github/servo/surfman/builds/177861097. It used to complete without issue, and now it gives this output:

error: failed to read `/home/travis/.rustup/toolchains/nightly-2020-07-29-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/Cargo.toml`

Caused by:

  No such file or directory (os error 2)

The command "cargo build -Z build-std --verbose --target=aarch64-uwp-windows-msvc" exited with 101.

[jdm]

This may be a regression in the rust-src bundle somehow. This affects the CI on all of Linux, macOS, and Windows.

[alexcrichton]

I believe this was already fixed in #8558 and rust-lang/rust was updated today in rust-lang/rust#74923