Bug 1829051 - Add clang path to $PATH during the build for mac builds. r=firefox-build-system-reviewers,andi

While here, replace the manual split of os.environ["PATH"] with
original_path, which is the same thing.

Differential Revision: https://phabricator.services.mozilla.com/D178408

build/moz.configure/toolchain.configure

@@ -721,11 +721,18 @@ def rust_search_path(rust_path, search_order, original_path):
 # Prepend the mozilla-build msys2 path, since otherwise we can get mismatched
 # cygwin dll errors during configure if we get called from another msys2
 # environment, see bug 1801826.
-@depends(mozillabuild_bin_paths)
+@depends(mozillabuild_bin_paths, clang_search_path, target, original_path)
 @imports("os")
-def altered_path(mozillabuild_bin_paths):
+def altered_path(mozillabuild_bin_paths, clang_search_path, target, original_path):
     altered_path = mozillabuild_bin_paths
-    for p in os.environ["PATH"].split(os.pathsep):
+    if target.kernel == "Darwin":
+        # The rust compiler wants to execute dsymutil, but it does so in a
+        # non-configurable way (https://github.com/rust-lang/rust/issues/52728)
+        # so we add the clang path.
+        path = clang_search_path
+    else:
+        path = original_path
+    for p in path:
         if p not in altered_path:
             altered_path.append(p)
     return os.pathsep.join(altered_path)