[clang] [Clang] Make the result type of sizeof/pointer subtraction/size_t lit… (PR #136542)

[John McCall via cfe-commits]

rjmccall wrote:

It's fine to make these operators look up and use the `size_t` / `ptrdiff_t` typedefs if they're available and have the right type. We would need to apply an allowlist to the attributes on the typedef, too — it would be quite abusive, but someone could use an `aligned` attribute on their `size_t` typedef, and that would be wrong. But once we've successfully done the lookup and associated checks, we can cache the result.

We can't use a canonically different type.

https://github.com/llvm/llvm-project/pull/136542