[libc++] When run in verbose mode, ssh.py should print to stderr, not stdout

Otherwise this can mess up the test results which inspect stdout.
diff --git a/libcxx/utils/ssh.py b/libcxx/utils/ssh.py
index 3f0e2f3..e1eaa5a 100755
--- a/libcxx/utils/ssh.py
+++ b/libcxx/utils/ssh.py
@@ -53,7 +53,7 @@
 
     def runCommand(command, *args_, **kwargs):
         if args.verbose:
-            print(f"$ {' '.join(command)}")
+            print(f"$ {' '.join(command)}", file=sys.stderr)
         return subprocess.run(command, *args_, **kwargs)
 
     # Create a temporary directory where the test will be run.