[libcxx] Don't pass -s to libtool

This flag is the default in libtool on Darwin, and it's not supported
by llvm-libtool-darwin causing a build failure.

Differential Revision: https://reviews.llvm.org/D88449

libcxx/utils/merge_archives.py

@@ -143,7 +143,7 @@ def main():
 
     if args.use_libtool:
         files = [f for f in files if not f.startswith('__.SYMDEF')]
-        execute_command_verbose([libtool_exe, '-static', '-o', args.output, '-s'] + files,
+        execute_command_verbose([libtool_exe, '-static', '-o', args.output] + files,
                                 cwd=temp_directory_root, verbose=args.verbose)
     else:
         execute_command_verbose([ar_exe, 'rcs', args.output] + files,