Support excluding harness files from the unused includes check

tools/lint/lib/checks/includes.py

@@ -22,10 +22,14 @@ def _load(include_name):
             with open(os.path.join('harness', include_name), 'r') as f:
                 source = f.read()
 
+            parsed = parse(source)
+            if not parsed:
+                raise Exception(f"Failed to parse {include_name}")
             CheckIncludes._cache[include_name] = {
                 'name': include_name,
                 'source': CheckIncludes._remove_frontmatter(source),
-                'defines': parse(source)['defines']
+                'defines': parsed['defines'],
+                'allow_unused': parsed.get('allow_unused', False),
             }
 
         return CheckIncludes._cache.get(include_name)
@@ -57,6 +61,9 @@ def run(self, name, meta, source):
         without_frontmatter = self._remove_frontmatter(source)
 
         for harness_file in harness_files:
+            if harness_file['allow_unused']:
+                continue
+
             if self._has_reference(without_frontmatter, harness_file['defines']):
                 continue