REALLOCARRAY: apply OpenBSD's fix.

in some architectures, shifting with 1UL could lead to overflow. size_t is platform dependant, so we re quite safe.

Signed-off-by: Shawn Webb <lattera@gmail.com>
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/userlandenhanced
Merge remote-tracking branch 'origin/hardened/current/userlandenhanced' into hardened/current/unstable