UIC-8953: rust: Trace cargo and allow target triple overide

This change is helpful to trace/debug rust related job.
This was useful to build zpc natively on arm64 (aarch64-unknown-linux-gnu).

What has been observed on native arm64 build:

    .../1.71.0-aarch64-unknown-linux-gnu/bin/cargo build \
   --manifest-path /.../applications/zpc/components/zpc_rust/Cargo.toml \
   --locked \
   --target x86_64-unknown-linux-gnu

While it was passed a cmake define

It was made for core v7 but also applies to zpc v6

Relate-to: https://doc.rust-lang.org/nightly/rustc/platform-support.html
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

cmake/modules/CargoMeta.cmake

@@ -357,7 +357,11 @@ function(rust_is_configured_for_deb CARGO_META_PACKAGE CONFIGURED)
   endif()
 endfunction()
 
-get_target_triple(CARGO_TARGET_TRIPLE)
+# Allow overide from env (the above detection may not be reliable or scale)
+if(NOT DEFINED CARGO_TARGET_TRIPLE)
+  get_target_triple(CARGO_TARGET_TRIPLE)
+endif()
+
 set(DIR_OF_CARGO_META
     ${CMAKE_CURRENT_LIST_DIR}
     CACHE INTERNAL "DIR_OF_CARGO_META")
@@ -369,7 +373,9 @@ function(rust_workspace_metadata CARGO_MANIFEST_DIR CARGO_METADATA)
         ${CARGO_EXECUTABLE} "metadata" "--manifest-path"
         "${CARGO_MANIFEST_DIR}/Cargo.toml" "--format-version" "1"
         "--filter-platform" "${CARGO_TARGET_TRIPLE}"
-      OUTPUT_VARIABLE METADATA COMMAND_ERROR_IS_FATAL ANY)
+      OUTPUT_VARIABLE METADATA COMMAND_ERROR_IS_FATAL ANY
+      COMMAND_ECHO STDERR
+)
     set(${CARGO_METADATA}
         ${METADATA}
         PARENT_SCOPE)