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

[Hans Wennborg via cfe-commits]

zmodem wrote:

I haven't dug into the details (and don't know much about WinEH), but we just bisected a Rust test failure to this revision. After this, https://github.com/rust-lang/rust/blob/213d946a384b46989f6fd9c8ae9c547b4e354455/tests/ui/asm/x86_64/may_unwind.rs fails on Windows.

Do folks on this PR have any ideas on what might be going wrong? For example, does Rust need to adapt its llvm codegen for this in some way? Or does the test do something that looks bad?

(Our ref: https://crbug.com/436652831)

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