[compiler-rt] [scudo] Handle failed mmap for allocation ring buffer (PR #71817)

[Mitch Phillips via llvm-commits]

https://github.com/hctim approved this pull request.

Also `unmapRingBuffer()` and `getRingBufferErrorInfo()` (latter is unrelated but could be more defensive)?

Otherwise LGMT

https://github.com/llvm/llvm-project/pull/71817