rust: Oe-selftest changes for rust v1.77

rust: Oe-selftest changes for rust v1.77

    Update the file paths for v1.77 and fix the dead code error as follows:

    Compiling coverage-dump v0.1.0 (/home/poky/build-st/tmp/work/core2-64-poky-linux/rust/1.77.0/rustc-1.77.0-src/src/tools/coverage-dump)
    error: field `0` is never read
       --> src/tools/coverage-dump/src/covfun.rs:222:15
        |
    222 |     Expansion(u32),
        |     --------- ^^^
        |     |
        |     field in this variant
        |
        = note: `-D dead-code` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(dead_code)]`
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    222 |     Expansion(()),
        |               ~~

    error: could not compile `coverage-dump` (bin "coverage-dump") due to 1 previous error

    Only the required change is backported here to run the build without any errors.
    Other changes are merged with the commit in v1.78.

    Reference: https://github.com/rust-lang/rust/commit/9a5034a20ed8b055dc615271f9d9cf27f9e494f0#diff-d4ecc6273352a2a8ebd02c45233d9bff7c6694f20b67ddad0614af7a89c06748

Signed-off-by: Yash Shinde <Yash.Shinde@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>