Add support for cross-compiled binaries

[harrisonmg]

Cargo puts cross-compiled binaries in an additional subdirectory; for example:

native: target/debug
vs
arm64: target/aarch64-unknown-linux-gnu/debug

For this reason, cargo-ament-build fails when cross compiling:

Starting >>> publ
--- stderr: publ
Error in cargo-ament-build

Caused by:
0: Failed to copy binary from '/workspace/build/publ/debug/publ'
1: No such file or directory (os error 2)
---
Failed   <<< publ [5.09s, exited with code 1]

This change introduces detection of the build target architecture via the --target argument or the CARGO_BUILD_TARGET environment variable and modifies the search path for binaries accordingly.

[luca-della-vedova]

Thanks for the contribution!

Makes sense to me, I haven't tried on cargo-ament-build but I tested on a cargo build in cross compiling and I do see the folder structure you mentioned so the implementation looks correct.
I'll approve first, I'll give it a few days if any other maintainer wants to give it a look then merge it if there is no opposition.

[esteve]

@harrisonmg LGTM, thanks!

[esteve]

@luca-della-vedova thanks for having a look, I'll go and merge this PR