Commit 8cce08f1 used a left-shift
on a literal of 1 that could (in large allocations) be shifted by
31 or more bits.  This was assigned to a local variable that was
already declared to be a long to protect against overruns of int,
but the literal in this shift needs to be declared long to allow it
to work correctly in some compilers.

Backpatch to 9.5, where the bug was introduced.

Report and patch by KaiGai Kohei, slighly modified based on
discussion.