lit: print process output, if getting the list of google-tests failed.

[krasin]

Summary

This is a follow up to r280455, where a check for the process exit code
was introduced. Some ASAN bots throw this error now, but it's impossible
to understand what's wrong with them, and the issue is not reproducible.

llvm/trunk/utils/lit/lit/formats/googletest.py

 from __future__ import absolute_import
 import os
+import subprocess
 import sys
 
 import lit.Test
 import lit.TestRunner
 import lit.util
 from .base import TestFormat
 
 kIsWindows = sys.platform in ['win32', 'cygwin']
def getGTestTests(self, path, litConfig, localConfig):
           localConfig: TestingConfig instance"""
 
         try:
             lines = lit.util.capture([path, '--gtest_list_tests'],
                                      env=localConfig.environment)
             if kIsWindows:
               lines = lines.replace('\r', '')
             lines = lines.split('\n')
-        except:
-            litConfig.error("unable to discover google-tests in %r: %s"
-                            % (path, sys.exc_info()[1]))
+        except Exception as exc:
+            out = exc.output if isinstance(exc, subprocess.CalledProcessError) else ''
+            litConfig.error("unable to discover google-tests in %r: %s. Process output: %s"
+                            % (path, sys.exc_info()[1], out))
             raise StopIteration
 
         nested_tests = []
         for ln in lines:
             if not ln.strip():
                 continue
 
             if 'Running main() from gtest_main.cc' in ln:
def execute(self, test, litConfig):
 
         passing_test_line = '[  PASSED  ] 1 test.'
         if passing_test_line not in out:
             msg = ('Unable to find %r in gtest output:\n\n%s%s' %
                    (passing_test_line, out, err))
             return lit.Test.UNRESOLVED, msg
 
         return lit.Test.PASS,''
-

llvm/trunk/utils/lit/lit/util.py

except OSError:
             raise
 
 def capture(args, env=None):
     """capture(command) - Run the given command (or argv list) in a shell and
     return the standard output. Raises a CalledProcessError if the command
     exits with a non-zero status."""
     p = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                          env=env)
-    out,_ = p.communicate()
+    out, err = p.communicate()
+    out = convert_string(out)
+    err = convert_string(err)
     if p.returncode != 0:
-        raise subprocess.CalledProcessError(cmd=args, returncode=p.returncode)
+        raise subprocess.CalledProcessError(cmd=args,
+                                            returncode=p.returncode,
+                                            output="{}\n{}".format(out, err))
     return convert_string(out)
 
 def which(command, paths = None):
     """which(command, [paths]) - Look up the given command in the paths string
     (or the PATH environment variable, if unspecified)."""
 
     if paths is None:
         paths = os.environ.get('PATH','')