Bug 1823058 - Fix WindowsPath related TypeErrors from mach build. r=glandium

Differential Revision: https://phabricator.services.mozilla.com/D172889

python/mozbuild/mozbuild/action/file_generate_wrapper.py

@@ -20,12 +20,12 @@ def action(fh, script, target_dir, *args):
     topsrcdir = Path(buildconfig.topsrcdir)
 
     def make_absolute(base_path, p):
-        return base_path / p[1:] if p.startswith("/") else base_path / p
+        return Path(base_path) / Path(p.lstrip("/"))
 
     try:
-        abs_target_dir = make_absolute(objdir, target_dir)
+        abs_target_dir = str(make_absolute(objdir, target_dir))
         abs_script = make_absolute(topsrcdir, script)
-        script = [abs_script]
+        script = [str(abs_script)]
         if abs_script.suffix == ".py":
             script = [sys.executable] + script
         subprocess.check_call(script + args, cwd=abs_target_dir)