apps/tools: Enable Rust sim builds on Intel Macs

[toku-mac]

Summary

Make the Rust app build pick the correct x86_64 target triple for the NuttX simulator on Intel macOS.
This complements the corresponding nuttx repo change that adds the x86_64 Mach-O Rust target.

Testing

I confirm that changes are verified on local setup and works as intended:

• Build Host(s): OS (macOS 14.8), CPU(Intel Core i7), compiler(Apple clang version 16.0.0)
• Target(s): arch(sim)
• Ensure your PATH environment variable is properly configured to allow execution of: menuconfig, olddefconfig, savedefconfig, and setconfig.
• Use the Rust toolchain version prior to nightly-2026-04-29 to avoid errors related to lib/rustlib/src/rust/library/std/src/sys/net/connection/socket/unix.rs.
• Depends on the corresponding nuttx side PR. #19058

PR verification Self-Check

• My PR adheres to Contributing Guidelines and Documentation (git commit title and message, coding standard, etc).
• My PR is ready for review and can be safely merged into a codebase.

[toku-mac]

Is there a network problem with the CI machine?

Build / Linux (sim-03) (pull_request)Failing after 40m

error: downloading 'https://github.com/OpenAMP/open-amp/archive/v2025.10.0.zip' failed
   status_string: "HTTP response code said error"
The requested URL returned error: 504
CMake Error ... Build step for open-amp failed: 1
...
ninja: error: loading 'build.ninja': No such file or directory

[lupyuen]

GitHub Actions was having problems earlier today: https://www.githubstatus.com/incidents/m7n7sm0sr1pz

https://lupyuen.github.io/nuttx-github-jobs/build-monitor

[lupyuen]

@no1wudi Could you review this PR? Thanks :-)