ModuleInstance.Closed is an atomic variable meant to be loaded and
swapped with sync/atomic. Closed, being a 64 bit integer, requires 64
bit alignment. The simplest way we can get alignment is to place these
atomic fields at the top of their struct.
Closed can be moved to a more logical place once support for Go 1.18 is
dropped and its type changed to atomic.Uint64.
Signed-off-by: Tristan Willy <tristan.willy@gmail.com>
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