Repeated "warning: profiles for the non root package will be ignored" when building Rust

[SimonSapin]

Sample output while in the middle of working on something:

% ./x.py build
Updating submodules
warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/simon/rust3/src/tools/cargo/Cargo.toml
workspace: /home/simon/rust3/src/Cargo.toml
    Finished dev [unoptimized] target(s) in 0.0 secs
warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/simon/rust3/src/tools/cargo/Cargo.toml
workspace: /home/simon/rust3/src/Cargo.toml
warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/simon/rust3/src/tools/cargo/Cargo.toml
workspace: /home/simon/rust3/src/Cargo.toml
warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/simon/rust3/src/tools/cargo/Cargo.toml
workspace: /home/simon/rust3/src/Cargo.toml
Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/simon/rust3/src/tools/cargo/Cargo.toml
workspace: /home/simon/rust3/src/Cargo.toml
   Compiling alloc v0.0.0 (file:///home/simon/rust3/src/liballoc)
   Compiling alloc_system v0.0.0 (file:///home/simon/rust3/src/liballoc_system)
[…]

15 of the 18 first lines of output are effectively noise due to this warning.

Indeed, src/tools/cargo/Cargo.toml contains:

[profile.release]
overflow-checks = true

But this same Cargo.toml file is both the root of a workspace when the cargo repository is used on its own, and a member of a larger workspace when use like here as a submodule of the rust repository. So this [profile] section is both sometimes significant (and perhaps should not be remove) and sometimes not (so the warning is not a false-positive).

Should there be an exception list to silence this somewhat verbose warning? Or is this not worth doing without fixing the underlying issue: adding a mechanism for enabling overflow checking per-crate rather than per-workspace? (Is there a tracking issue for that? It is close to but not quite rust-lang/cargo#1359.)

[SimonSapin]

src/tools/cargo/Cargo.toml no longer contains a profile section.