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

[Rainer Orth via cfe-commits]

rorth wrote:

No, that doesn't exist.  The failure will occur on any non-x86 build configure with `-DLLVM_TARGETS_TO_BUILD=<anything not including X86>`.

AFAICS the tests just need
```
// REQUIRES: x86-registered-target
```

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