[libcxx] [llvm] [libc++][AIX] Fix force_thread_creation_failure by using RLIMIT_THREADS (PR #188787)

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Himadhith wrote:

@philnik777 Sure, I'll revert the PR. But what about the other PR which was added to fix stray binary? Should I revert that as well?

https://github.com/llvm/llvm-project/pull/188787