[clang-tidy] Use raw string for regex pattern

Author: wonbinbk

clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py

@@ -247,7 +247,7 @@ def main():
     filename = None
     lines_by_file = {}
     for line in sys.stdin:
-        match = re.search('^\\+\\+\\+\\ "?(.*?/){%s}([^ \t\n"]*)' % args.p, line)
+        match = re.search(r'^\+\+\+\ "?(.*?/){%s}([^ \t\n"]*)' % args.p, line)
         if match:
             filename = match.group(2)
         if filename is None: