[clang] [Clang] Generate the GEP instead of adding AST nodes (PR #73730)

[Bill Wendling via cfe-commits]

bwendling wrote:

The `__bdos` stuff is only a subset of the bounds checking code so we should focus on that.

It's still messier than that, since it's not always going to be a pointer directly to the FAM (e.g. p->a.b.c.array[index]), but I'll give it a shot. I don't think it's going to be any less convoluted.

https://github.com/llvm/llvm-project/pull/73730