[clang] [compiler-rt] [clang][UBSan] Add implicit conversion check for bitfields (PR #75481)

[John McCall via cfe-commits]

rjmccall wrote:

> @rjmccall fixed feedback
> 
> > You should handle compound assignments.
> 
> I believe I already support compound assignments (and PrePostIncDec), if I am not missing something? 😃

Ah, maybe you are, sorry.  I was expecting it in `CGExpr.cpp` and forgot that that code was actually in `CGExprScalar.cpp`.

https://github.com/llvm/llvm-project/pull/75481