When a MIR argument is spread at ABI level, deduced attributes are
potentially misapplied, since a spread argument can correspond to zero
or more arguments at ABI level.
Disable deduction for MIR using spread argument for the time being.
Extend attribute deduction to determine whether parameters using
indirect pass mode might have their address captured. Similarly to
the deduction of `readonly` attribute this information facilitates
memcpy optimizations.
