[compiler-rt] Use --standalone when running tests on the iOS simulator

[yln]

Summary

We can use simctl spawn --standalone to enable running tests without
the need for an already-booted simulator instance. This also side-steps
the problem of not having a good place to shutdown the instance after
we are finished with testing.

rdar://58118442

[yln]

Also remove check for env var.

[yln]

compiler-rt/test/sanitizer_common/ios_commands/iossim_prepare.py

10

Note that we still have this check in iossim_run.py.

compiler-rt/test/sanitizer_common/ios_commands/iossim_prepare.py

 #!/usr/bin/python
 
 import json
-import os
-import subprocess
-
-
-device_id = os.environ.get('SANITIZER_IOSSIM_TEST_DEVICE_IDENTIFIER')
-if not device_id:
-    raise EnvironmentError('Specify SANITIZER_IOSSIM_TEST_DEVICE_IDENTIFIER to select which simulator to use.')
-
-DEVNULL = open(os.devnull, 'w')
-subprocess.call(['xcrun', 'simctl', 'shutdown', device_id], stderr=DEVNULL)
-subprocess.check_call(['xcrun', 'simctl', 'boot', device_id])
-# TODO(rdar58118442): we start the simulator here, but we never tear it down
-
 
 print(json.dumps({"env": {}}))

compiler-rt/test/sanitizer_common/ios_commands/iossim_run.py

for arg in sys.argv[2:]:
     else:
       # FIXME(dliew): pipes.quote() is deprecated
       rm_args.append(pipes.quote(arg))
   rm_cmd_line = ["/bin/rm"] + rm_args
   rm_cmd_line_str = ' '.join(rm_cmd_line)
   # We use `shell=True` so that any wildcard globs get expanded by the shell.
   exitcode = subprocess.call(rm_cmd_line_str, shell=True)
 else:
-  exitcode = subprocess.call(["xcrun", "simctl", "spawn", device_id] + sys.argv[1:])
+  exitcode = subprocess.call(["xcrun", "simctl", "spawn", "--standalone", device_id] + sys.argv[1:])
 if exitcode > 125:
   exitcode = 126
 sys.exit(exitcode)