RTS: Fix restrictive cast
Commit e75a9afd 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).