use blead linux/hints.sh
Avoid wraparound when casting unsigned size_t to signed ssize_t.

Practically, this only affects a perl compiled with 64-bit IVs on a 32-bit
system.  In that instance a value of count >= 2**31 would turn negative
when cast to (ssize_t).
(cherry picked from commit 94e529cc4d56863d7272c254a29eda2b002a4335)
Prevent premature hsplit() calls, and only trigger REHASH after hsplit()

Triggering a hsplit due to long chain length allows an attacker
to create a carefully chosen set of keys which can cause the hash
to use 2 * (2**32) * sizeof(void *) bytes ram. AKA a DOS via memory
exhaustion. Doing so also takes non trivial time.

Eliminating this check, and only inspecting chain length after a
normal hsplit() (triggered when keys>buckets) prevents the attack
entirely, and makes such attacks relatively benign.

(cherry picked from commit f14269908e5f8b4cab4b55643d7dd9de577e7918)
(which was itself cherry picked from commit f2a571dae7d70f7e3b59022834d8003ecd2df884)
(which was itself cherry picked (with changes) from commit f1220d61455253b170e81427c9d0357831ca0fac)