[clang] [clang][bytecode] Implement arithmetic, bitwise and compound assignment operator (PR #108949)

[Rainer Orth via cfe-commits]

rorth wrote:

This is weird: I'd initially tried both all-targets and sparc-only builds, and in neither case did the failures occur.  However, those were 2-stage builds (as I usually use).  When I switched to a 1-stage build with `clang-19` as build compiler, I get the same failure as on the bot locally, so this isn't just a quirk of the bot build environment.

https://github.com/llvm/llvm-project/pull/108949