[lldb] Change directory creation logic in framework-header-fix (#158355)

It's possible for this logic to fail if the build system runs this
script in parallel. One instance could create the directory in between
another instance's checking of its existence and attempt at creation.

Instead, always try to create it and ignore any FileExistsErrors.

rdar://160120161

lldb/scripts/framework-header-fix.py

@@ -115,8 +115,10 @@ def main():
         unifdef_guards = ["-U" + guard for guard in args.unifdef_guards]
 
     # Create the framework's header dir if it doesn't already exist
-    if not os.path.exists(os.path.dirname(output_file_path)):
+    try:
         os.makedirs(os.path.dirname(output_file_path))
+    except FileExistsError:
+        pass
 
     if framework_version == "lldb_main":
         modify_main_includes(input_file_path, output_file_path)