Confusing suggestion to use `cargo:rustc-link-lib` in a cargo project with a lib and bins about rust HOT 4 OPEN

  = note: /usr/bin/ld: /tmp/cargo-build-linking-bug/linking-with-lib-doesnt/target/debug/deps/buildrs_linking_bug-87372c54d74efe55.6x51e5ear2x9hplszhwkzwe3l.rcgu.o: in function `buildrs_linking_bug::main':
          /tmp/cargo-build-linking-bug/linking-with-lib-doesnt/src/main.rs:6: undefined reference to `my_custom_fn'
          collect2: error: ld returned 1 exit status

  = note: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib)

warning: `buildrs-linking-bug` (bin "buildrs-linking-bug") generated 1 warning
error: could not compile `buildrs-linking-bug` (bin "buildrs-linking-bug") due to 1 previous error; 1 warning emitted

 = note: /usr/bin/ld: /tmp/cargo-build-linking-bug/linking-with-lib-doesnt/target/debug/deps/buildrs_linking_bug-87372c54d74efe55.6x51e5ear2x9hplszhwkzwe3l.rcgu.o: in function `buildrs_linking_bug::main':
          /tmp/cargo-build-linking-bug/linking-with-lib-doesnt/src/main.rs:6: undefined reference to `my_custom_fn'
          collect2: error: ld returned 1 exit status

  = note: Your package has both a binary and library target. Since  the library has access to the symbols from the given lib, the binary should access them through the library target’s public API. (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib)