RTS: Fix restrictive cast

Commit e75a9afd2989e0460f9b49fa07c1667299d93ee9 added an `unsigned` cast
to account for OSes that have signed `rlim_t` signed. Unfortunately,
the `unsigned` cast has the unintended effect of narrowing `rlim_t` to
only 4 bytes. This leads to some spurious out of memory crashes
(in particular: Haddock crashes with OOM whenn building docs of
`ghc`-the-library).

In this case, `W_` is a better type to cast to: we know it will be
unsigned too and it has the same type as `*len` (so we don't suffer from
accidental narrowing).

0 files changed, 0 insertions, 0 deletions