apps/cmake: Fix aarch64 NuttX Rust target specs

[toku-mac]

Summary

Previously, aarch64 sim builds on macOS used aarch64-apple-darwin,
which sets target_os=macos and causes NuttX-specific cfg guards to be silently skipped.

This PR adds two custom Rust target JSON files:

• tools/aarch64-unknown-nuttx.json — ELF target for Linux/bare-metal
• tools/aarch64-unknown-nuttx-macho.json — Mach-O target for macOS sim

Rust.mk and cmake/nuttx_add_rust.cmake are updated to select the
appropriate target.

Depends on the corresponding nuttx-side PR. #18992

Impact

Allows proper building of sim on Apple Silicon Macs and aarch64 Linux.
(Support for Intel Macs will be considered separately.)

Testing

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

• Build Host(s): OS (macOS 26.5), CPU(Apple M1), compiler(Apple clang version 21.0.0)
• 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.
• This PR is a successor of PR #18978

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.

[xiaoxiang781216]

should we reuse the same file from nuttx git?

[toku-mac]

Is your intention the same as the patch below?
Also, should I move tools/aarch64-unknown-nuttx.json to the nuttx git as well?

diff --git a/cmake/nuttx_add_rust.cmake b/cmake/nuttx_add_rust.cmake
index dfa91c31c..2c28983f0 100644
--- a/cmake/nuttx_add_rust.cmake
+++ b/cmake/nuttx_add_rust.cmake
@@ -57,7 +57,8 @@ function(nuttx_rust_target_triple ARCHTYPE ABITYPE CPUTYPE OUTPUT)
     set(TARGET_TRIPLE "${APPDIR}/tools/i486-unknown-nuttx.json")
   elseif(ARCHTYPE STREQUAL "aarch64")
     if(CONFIG_ARCH_SIM AND CONFIG_HOST_MACOS)
-      set(TARGET_TRIPLE "${APPDIR}/tools/aarch64-unknown-nuttx-macho.json")
+      set(TARGET_TRIPLE
+          "${PROJECT_SOURCE_DIR}/tools/aarch64-unknown-nuttx-macho.json")
     else()
       set(TARGET_TRIPLE "${APPDIR}/tools/aarch64-unknown-nuttx.json")
     endif()
diff --git a/tools/Rust.mk b/tools/Rust.mk
index 9ca03bdac..4fc74af4e 100644
--- a/tools/Rust.mk
+++ b/tools/Rust.mk
@@ -56,7 +56,7 @@ $(or \
   ), \
   $(and $(filter aarch64,$(LLVM_ARCHTYPE)), \
     $(if $(and $(filter sim,$(CONFIG_ARCH)),$(filter y,$(CONFIG_HOST_MACOS))), \
-      $(APPDIR)/tools/aarch64-unknown-nuttx-macho.json, \
+      $(TOPDIR)/tools/aarch64-unknown-nuttx-macho.json, \
       $(APPDIR)/tools/aarch64-unknown-nuttx.json \
     ) \
   ), \

[toku-mac]

Since the PR on the nuttx git repository has been merged into master, I've decided not to move the tools/aarch64-unknown-nuttx.json file from the apps git.
Please review commit 6e58319.