[llvm] [StringMap] Invalidate iterators on mutation (PR #202237)

[Adrian Prantl via llvm-commits]

adrian-prantl wrote:

Hi @MaskRay, I had to revert this and one follow-up commit because it broke the LLDB test suite, see https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/lldb-cmake/22124/

https://github.com/llvm/llvm-project/pull/202237