[libc] Fix definition of `UINT_MAX` in limits.h (#95279)

Summary:
Currently we use `(~0U)` for this definition, however the ~ operator
returns a different sign, meaning that preprocessor checks against this
value will fail. See https://godbolt.org/z/TrjaY1d8q where the
preprocessor thinks that it's not `0xffffffff` while the static
assertion thinks it is. This is because the latter does implicit
conversion but the preprocessor does not. This is now consistent with
other headers.