fix(rules): improve linker PATH construction for Windows and macOS

Improved `get_linking_path` to ensure essential system paths are available
during the linking stage, fixing build failures on Windows and macOS (Intel).

- Included `C:\Windows\System32` and `C:\Windows` for Windows builds.
- Implemented path deduplication to keep the `PATH` environment clean.
- Added robust directory extraction handling both `/` and `\` separators.
- Updated Starlark unit tests to verify the new path construction logic.

Fixes #11

Author: meisam

scala_native/private/rules/target_triple.bzl

@@ -98,14 +98,33 @@ def get_linking_path(host_path_separator, clang_path, ar_path):
     Returns:
         A string containing the PATH environment variable.
     """
-    paths = [
-        clang_path.rpartition("/")[0],
-        ar_path.rpartition("/")[0],
-    ]
-
-    # Add standard paths on POSIX for tools that might be needed by the linker
+    # Use a dict to deduplicate paths while preserving order
+    unique_paths = {}
+
+    def add_path(p):
+        if p and p not in unique_paths:
+            unique_paths[p] = True
+
+    def get_dir(p):
+        # Bazel usually uses forward slashes even on Windows, but check for both.
+        # rpartition returns (before, separator, after)
+        for sep in ["/", "\\"]:
+            before, s, _ = p.rpartition(sep)
+            if s:
+                return before
+        return ""
+
+    add_path(get_dir(clang_path))
+    add_path(get_dir(ar_path))
+
+    # Add standard paths for tools that might be needed by the linker
     # discovery but are not part of the hermetic toolchain (e.g. system libs)
     if host_path_separator == ":":
-        paths.extend(["/usr/bin", "/bin"])
-
-    return host_path_separator.join(paths)
+        add_path("/usr/bin")
+        add_path("/bin")
+    elif host_path_separator == ";":
+        # Standard Windows system paths
+        add_path("C:\\Windows\\System32")
+        add_path("C:\\Windows")
+
+    return host_path_separator.join(unique_paths.keys())

tests/unit/target_triple_test.bzl

@@ -320,13 +320,13 @@ _platform_flags_none_triple_test = unittest.make(
 
 def _linking_path_posix_test_impl(ctx):
     env = unittest.begin(ctx)
-    # POSIX uses ':' and includes /usr/bin, /bin
+    # POSIX uses ':' and includes /usr/bin, /bin. It should also deduplicate.
     result = get_linking_path(
         ":",
         "/path/to/llvm/bin/clang",
         "/path/to/llvm/bin/ar",
     )
-    asserts.equals(env, "/path/to/llvm/bin:/path/to/llvm/bin:/usr/bin:/bin", result)
+    asserts.equals(env, "/path/to/llvm/bin:/usr/bin:/bin", result)
     return unittest.end(env)
 
 _linking_path_posix_test = unittest.make(
@@ -335,13 +335,13 @@ _linking_path_posix_test = unittest.make(
 
 def _linking_path_windows_test_impl(ctx):
     env = unittest.begin(ctx)
-    # Windows uses ';' and should NOT include /usr/bin, /bin
+    # Windows uses ';' and should include System32, and deduplicate.
     result = get_linking_path(
         ";",
         "C:/llvm/bin/clang.exe",
         "C:/llvm/bin/llvm-ar.exe",
     )
-    asserts.equals(env, "C:/llvm/bin;C:/llvm/bin", result)
+    asserts.equals(env, "C:/llvm/bin;C:\\Windows\\System32;C:\\Windows", result)
     return unittest.end(env)
 
 _linking_path_windows_test = unittest.make(
@@ -362,6 +362,22 @@ _linking_path_different_dirs_test = unittest.make(
     _linking_path_different_dirs_test_impl,
 )
 
+def _linking_path_dedup_test_impl(ctx):
+    env = unittest.begin(ctx)
+    # Test that duplicate paths are removed even if they come from different sources
+    result = get_linking_path(
+        ":",
+        "/usr/bin/clang",
+        "/usr/bin/ar",
+    )
+    # /usr/bin is added by clang/ar paths AND by default POSIX paths, should only appear once.
+    asserts.equals(env, "/usr/bin:/bin", result)
+    return unittest.end(env)
+
+_linking_path_dedup_test = unittest.make(
+    _linking_path_dedup_test_impl,
+)
+
 # ===========================================================================
 # Test suite entry point
 # ===========================================================================
@@ -404,4 +420,5 @@ def target_triple_test_suite(name):
         _linking_path_posix_test,
         _linking_path_windows_test,
         _linking_path_different_dirs_test,
+        _linking_path_dedup_test,
     )