[clang-tidy] check_clang_tidy.py: Print output nicely in Python 3.

[PiotrZSL]

Summary

In Python 3, encode() produces a bytes. The way this is printed makes it
very hard to read the clang-tidy output because everything gets jammed onto one
line (newlines are printed as \n).

The encode() was introduced here:

https://github.com/llvm/llvm-project/commit/a35efc4dcb70658ebd704c28dfeed4cc2bac095b

It seems that this was done to print non-ASCII characters correctly in Python 2,
and this seems worth preserving (though anyone still on Python 2 should really
be migrating).

For the time being, I've simply introduced a version distinction. I'm not sure
if there's a more idiomatic way to do this that works in both Python 2 and
Python 3 -- input welcome!

[PiotrZSL]

Fixed by f7a80c3d08d4821e621fc88d6a2e435291f82dff

clang-tools-extra/test/clang-tidy/check_clang_tidy.py

class CheckRunner:
   def run_clang_tidy(self):
     args = ['clang-tidy', self.temp_file_name, '-fix', '--checks=-*,' + self.check_name] + \
         self.clang_tidy_extra_args + ['--'] + self.clang_extra_args
     if self.expect_clang_tidy_error:
       args.insert(0, 'not')
     print('Running ' + repr(args) + '...')
     clang_tidy_output = try_run(args)
     print('------------------------ clang-tidy output -----------------------')
+    if sys.version_info.major >= 3:
+      print(clang_tidy_output);
+    else:
       print(clang_tidy_output.encode())
     print('\n------------------------------------------------------------------')
 
     diff_output = try_run(['diff', '-u', self.original_file_name, self.temp_file_name], False)
     print('------------------------------ Fixes -----------------------------\n' +
           diff_output +
           '\n------------------------------------------------------------------')
     return clang_tidy_output