[llvm] [BOLT] Make .debug_names emission reproducible (PR #225218)

[Rafael Auler via llvm-commits]

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rafaelauler wrote:

I pushed a change to close one hole just in case (for split CU requesting a new synthesized name that happens to already exist in the main CU), although I didn't see it happening in my test inputs because we don't really synthesize new names other than "anonymous namespace".

https://github.com/llvm/llvm-project/pull/225218