Previously, the SpecificAllocator was a static local in the `make<T>`
function template. Using static locals is nice because they are only
constructed and registered if they are accessed. However, if there are
multiple calls to make<> with different constructor parameters, we would
get multiple static local variable instances. This is undesirable and
leads to extra memory allocations. I noticed there were two sources of
DefinedRegular allocations while checking heap profiles.
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