[llvm] [llvm-symbolizer] nfc, use map instead of vector (PR #69552)

[Chen Zheng via llvm-commits]

chenzheng1030 wrote:

gentle ping. (Sorry for ping this in less than a week. I am going to move forward for https://github.com/llvm/llvm-project/pull/69553. That patch solves some internal regressions.)

https://github.com/llvm/llvm-project/pull/69552