[compiler-rt] [compiler-rt] Fix definition of `uptr` (and `usize`) on 32-bit Windows (PR #106151)

[Alexander Richardson via llvm-commits]

arichardson wrote:

Looking into this a bit more, I feel that https://github.com/llvm/llvm-project/pull/106155 is a cleaner solution since it handles more architectures, but maybe best to land this in order to keep it easy to cherry-pick?

https://github.com/llvm/llvm-project/pull/106151