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

[Bill Wendling via cfe-commits]

bwendling wrote:

Closing in favor of https://github.com/llvm/llvm-project/pull/73730.

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