build-std: the build is broken after rust-lang/rust#73265

[JohnTitor]

Problem

Cargo now says when I use build-std feature with today(2020-07-29)'s nightly:

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

Caused by:
  No such file or directory (os error 2)

This assumes there're libstd and other paths but it has been changed in rust-lang/rust#73265:

cargo/src/cargo/core/compiler/standard_lib.rs

Lines 58 to 61 in 0d79ba6

	String::from("src/libstd"),
	String::from("src/libcore"),
	String::from("src/liballoc"),
	String::from("src/libtest"),

I think this should be also updated.

Steps

e.g. cargo build --target hexagon-unknown-linux-musl -Z build-std=core,alloc

Output of cargo version:

cargo 1.47.0-nightly (aa68721 2020-07-23)

[HarshitRuwali]

Facing the same error while pushing to Github, triggered by Actions. But works fine in my local machine.