[compiler-rt] Handle None value when polling addr2line pipe

[DavidSpickett]

Summary

According to:
https://docs.python.org/3/library/subprocess.html#subprocess.Popen.poll

poll can return None if the process hasn't terminated.

I'm not quite sure how addr2line could end up closing the pipe without
terminating but we did see this happen on one of our bots:

<...>scripts/asan_symbolize.py",
line 211, in symbolize
    logging.debug("addr2line exited early (broken pipe), returncode=%d"
% self.pipe.poll())
TypeError: %d format: a number is required, not NoneType

Handle None by printing a message that we couldn't get the return
code.

[DavidSpickett]

See https://lab.llvm.org/buildbot/#/builders/7/builds/2652

I presume this is a niche case, perhaps addr2line closes the pipe and is in the process of exiting by the time we poll(). If it had been later then it would work fine.
(and it looks like a transient error since there were no related changes in this build)

[delcypher]

compiler-rt/lib/asan/scripts/asan_symbolize.py

214

You don't need to do string interpolation here. You can just do

logging.debug("returncode=%d", self.pipe.poll())

even better yet

logging.debug("returncode={}".format(self.pipe.poll()))

which shouldn't care if self.pipe.poll() is not an integer.

I'm not sure if we've adopted python3 in this file yet but if we have then we could also do

logging.debug(f'returncode={self.pipe.poll()}')

[DavidSpickett]

Use f-string to format.

https://llvm.org/docs/GettingStarted.html#software requires
Python >=3.6 for the test suite and I can always fall back
to .format if bots break.

[delcypher]

LGTM

compiler-rt/lib/asan/scripts/asan_symbolize.py

try:
           logging.debug("got empty function and file name -> unknown function")
           function_name = '??'
           file_name = '??:0'
         lines.append((function_name, file_name))
     except IOError as e:
       # EPIPE happens if addr2line exits early (which some implementations do
       # if an invalid file is passed).
       if e.errno == errno.EPIPE:
-        logging.debug("addr2line exited early (broken pipe), returncode=%d" % self.pipe.poll())
+        logging.debug(f"addr2line exited early (broken pipe) returncode={self.pipe.poll()}")
       else:
         logging.debug("unexpected I/O exception communicating with addr2line", exc_info=e)
       lines.append(('??', '??:0'))
     except Exception as e:
       logging.debug("got unknown exception communicating with addr2line", exc_info=e)
       lines.append(('??', '??:0'))
     return ['%s in %s %s' % (addr, function, fix_filename(file)) for (function, file) in lines]
 
 class UnbufferedLineConverter(object):
   """
   Wrap a child process that responds to each line of input with one line of