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

[Alexander Richardson via llvm-commits]

arichardson wrote:

This seems to work on MSVC and MinGW: https://godbolt.org/z/s8YWaKaKn but I don't have an environment to test this.

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