implement easy solution

Author: vbvictor

clang/docs/tools/dump_ast_matchers.py

@@ -6,6 +6,7 @@
 import collections
 import re
 import os
+import sys
 
 try:
     from urllib.request import urlopen
@@ -615,5 +616,7 @@ def sort_table(matcher_type, matcher_map):
     flags=re.S,
 )
 
-with open(HTML_FILE, "w", newline="\n") as output:
+output_file = sys.argv[1] if len(sys.argv) == 2 else HTML_FILE
+
+with open(output_file, "w", newline="\n") as output:
     output.write(reference)

clang/test/AST/ast_matchers_updated.test

@@ -0,0 +1,2 @@
+// RUN: %python %S/../../docs/tools/dump_ast_matchers.py %t
+// RUN: diff %t %S/../../docs/LibASTMatchersReference.html