The intent here is to reuse the zone allocator for mozjemalloc, to avoid
all the shortcomings of mozjemalloc using a different one. This change
only moves the replace-malloc zone allocator out of replace-malloc.c, to
make changes for mozjemalloc integration clearer.
Somehow, we never called those hooks when replace-malloc is enabled. I'd
expect this to cause random deadlocks when forking, and I'm surprised
this hasn't surfaced. Maybe it actually causes some intermittent oranges
on automation, who knows.
This also brings consistency with what is done for jemalloc 4, and with
the mozjemalloc implementation, too, that we're going to replace with
this one in a subsequent changeset.
It appears to be an unnecessary optimization, since the compiler is still inlining
the functions when they're not marked static. OTOH, following patches will require
the _impl functions not to be static.
