[clang] [llvm] Fix Windows EH IP2State tables (remove +1 bias) (PR #144745)

[via cfe-commits]

sivadeilra wrote:

I've updated the comments and the PR description so that the tone is more neutral, and describes the state of LLVM after the PR, with less emphasis on LLVM's old behavior.

https://github.com/llvm/llvm-project/pull/144745