`packAndTransfer()` called `submitData()`, which captured the address of
the data of
the `SmallVector` member of `PrivateArgumentManagerTy`, as the host
source of an
async transfer. The manager was later moved into an `AsyncInfo`
post-processing
lambda, changing the underlying address of the data:
`addPostProcessingFunction()`
copies the closure rather than moving it, but even if it "moved", the
address of the data owned by `SmallVector`'s inline capacity would have
changed.
The AMDGPU plugin read from the stale host source address when doing the
actual transfer.
Fix: allocate the packed buffer via
`getOrCreateSourceBufferForSubmitData()`, so
that `AsyncInfo` owns it. The non-packed
corresponding-pointer-initialization
path in this same class already built its source buffer that way.
a1d93f19be