[libc++] Use proper shell escaping in the executors

This was originally committed as f8452ddfcc and reverted in 7cb1aa9d93.
The issue was that shell builtins were being escaped too, and apparently
Bash won't execute a builtin when it is quoted e.g. '!'. Instead, it
thinks it's a command and it can't find it.

Re-committing the change with that issue fixed.

libcxx/test/libcxx/selftest/newformat/shell-escape.sh.cpp

@@ -0,0 +1,18 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Make sure that arguments of the %{exec} substitution are shell-escaped
+// properly. If that wasn't the case, the command would fail because the
+// shell would look for a matching `"`.
+
+// RUN: %{exec} echo '"'
+
+// Also make sure that we don't escape Shell builtins like `!`, because the
+// shell otherwise thinks it's a command and it can't find it.
+
+// RUN: ! false

libcxx/utils/run.py

@@ -30,11 +30,11 @@ def main():
     if len(remaining) < 2:
         sys.stderr.write('Missing actual commands to run')
         exit(1)
-    remaining = remaining[1:] # Skip the '--'
+    commandLine = remaining[1:] # Skip the '--'
 
     # Do any necessary codesigning.
     if args.codesign_identity:
-        exe = remaining[0]
+        exe = commandLine[0]
         rc = subprocess.call(['xcrun', 'codesign', '-f', '-s', args.codesign_identity, exe], env={})
         if rc != 0:
             sys.stderr.write('Failed to codesign: ' + exe)
@@ -57,8 +57,8 @@ def main():
             else:
                 shutil.copy2(dep, args.execdir)
 
-        # Run the executable with the given environment in the execution directory.
-        return subprocess.call(' '.join(remaining), cwd=args.execdir, env=env, shell=True)
+        # Run the command line with the given environment in the execution directory.
+        return subprocess.call(subprocess.list2cmdline(commandLine), cwd=args.execdir, env=env, shell=True)
     finally:
         shutil.rmtree(args.execdir)
 

libcxx/utils/ssh.py

@@ -97,10 +97,11 @@ def main():
         # host by transforming the path of test-executables to their path in the
         # temporary directory, where we know they have been copied when we handled
         # test dependencies above.
+        commandLine = (pathOnRemote(x) if isTestExe(x) else x for x in commandLine)
         remoteCommands += [
             'cd {}'.format(tmp),
             'export {}'.format(' '.join(args.env)),
-            ' '.join(pathOnRemote(x) if isTestExe(x) else x for x in commandLine)
+            subprocess.list2cmdline(commandLine)
         ]
 
         # Finally, SSH to the remote host and execute all the commands.