[trans-mem] Fix outer transactions to be considered abortable too.

[Torvald Riegel <triegel at redhat dot com>]

Atomic transactions marked as outer(-atomic) transactions can abort too
if they are calling functions whose type has the may_cancel_outer
attribute. Given that outer transactions are probably rare, this patch
just assumes that all outer transactions might abort irrespective of
whether they are actually calling may_cancel_outer functions.
Previously, there was no abort-handling code generated for outer
transactions, except if there was a __transaction_cancel in lexical
scope.

OK for branch?

Attachment: patch3
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