[libcxx] [compiler-rt] [flang] [libc] [llvm] [clang] [Clang] Use correct base expression for counted_by field (#73168) (PR #73465)

[Nathan Chancellor via cfe-commits]

nathanchance wrote:

For what it's worth, this resolves both the issues that I reported at https://github.com/llvm/llvm-project/issues/73168, at least when building the full two files that I noticed had a problem before. I can do more builds later if necessary.

https://github.com/llvm/llvm-project/pull/73465