[libc++] [ssh] Fix tarring test dependencies on Windows

[broadwaylamb]

Summary

The motivation for this change is in the comment.

[ldionne]

After offline discussion with @broadwaylamb, we went ahead with b00a874b7c7371 instead. The main difference is that b00a874b7c7371 makes sure to close the NamedTemporaryFile before it tries to scp it, which is more in-line with the Python documentation:

Whether the name can be used to open the file a second time, while the named temporary file is still open, varies across platforms (it can be so used on Unix; it cannot on Windows NT or later).

libcxx/utils/ssh.py

def main():
     try:
         # Do any necessary codesigning of test-executables found in the command line.
         if args.codesign_identity:
             for exe in filter(isTestExe, commandLine):
                 subprocess.check_call(['xcrun', 'codesign', '-f', '-s', args.codesign_identity, exe], env={})
 
         # Ensure the test dependencies exist, tar them up and copy the tarball
         # over to the remote host.
-        with tempfile.NamedTemporaryFile(suffix='.tar') as tmpTar:
+        try:
+            with tempfile.NamedTemporaryFile(suffix='.tar', delete=False) as tmpTar:
                 with tarfile.open(fileobj=tmpTar, mode='w') as tarball:
                     for dep in args.dependencies:
                         if not os.path.exists(dep):
                             sys.stderr.write('Missing file or directory "{}" marked as a dependency of a test'.format(dep))
                             return 1
                         tarball.add(dep, arcname=os.path.basename(dep))
 
                 remoteTarball = pathOnRemote(tmpTar.name)
                 tmpTar.flush()
                 subprocess.check_call(scp(tmpTar.name, remoteTarball))
+        finally:
+            # We delete it manually because otherwise on Windows
+            # it gets deleted before we transfer it to the remote host.
+            # This is because on Windows, file handles with the O_TEMPORARY flag
+            # (which is set if we pass `delete=True`) are deleted as soon as
+            # they're closed.
+            os.remove(tmpTar.name)
 
         # Untar the dependencies in the temporary directory and remove the tarball.
         remoteCommands = [
             'tar -xf {} -C {}'.format(remoteTarball, tmp),
             'rm {}'.format(remoteTarball)
         ]
 
         # Make sure all test-executables in the remote command line have 'execute'