Revert "[lit] Use os.devnull instead of named temp files"

This reverts commit r272290. It breaks a test that depends on being able
to seek the /dev/null equivalent on Windows:

http://bb.pgr.jp/builders/ninja-clang-x64-mingw64-RA/builds/11360

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272293 91177308-0d34-0410-b5e6-96231b3b80d8

utils/lit/lit/TestRunner.py

@@ -20,6 +20,9 @@ kIsWindows = platform.system() == 'Windows'
 # Don't use close_fds on Windows.
 kUseCloseFDs = not kIsWindows
 
+# Use temporary files to replace /dev/null on Windows.
+kAvoidDevNull = kIsWindows
+
 class ShellEnvironment(object):
 
     """Mutable shell environment containing things like CWD and env vars.
@@ -189,6 +192,7 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
     input = subprocess.PIPE
     stderrTempFiles = []
     opened_files = []
+    named_temp_files = []
     # To avoid deadlock, we use a single stderr stream for piped
     # output. This is null until we have seen some output using
     # stderr.
@@ -252,8 +256,8 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
             else:
                 if r[2] is None:
                     redir_filename = None
-                    if kIsWindows and r[0] == '/dev/null':
-                        r[2] = open(os.devnull, r[1])
+                    if kAvoidDevNull and r[0] == '/dev/null':
+                        r[2] = tempfile.TemporaryFile(mode=r[1])
                     elif kIsWindows and r[0] == '/dev/tty':
                         # Simulate /dev/tty on Windows.
                         # "CON" is a special filename for the console.
@@ -302,11 +306,14 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
         if not executable:
             raise InternalShellError(j, '%r: command not found' % j.args[0])
 
-        if kIsWindows:
-            # Replace uses of /dev/null with the Windows equivalent.
+        # Replace uses of /dev/null with temporary files.
+        if kAvoidDevNull:
             for i,arg in enumerate(args):
                 if arg == "/dev/null":
-                    args[i] = os.devnull
+                    f = tempfile.NamedTemporaryFile(delete=False)
+                    f.close()
+                    named_temp_files.append(f.name)
+                    args[i] = f.name
 
         try:
             procs.append(subprocess.Popen(args, cwd=cmd_shenv.cwd,
@@ -415,6 +422,13 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
         else:
             exitCode = res
 
+    # Remove any named temporary files we created.
+    for f in named_temp_files:
+        try:
+            os.remove(f)
+        except OSError:
+            pass
+
     if cmd.negate:
         exitCode = not exitCode