swift234

[+0 self] Add the deallocating parameter convention.

The deallocating parameter convention is a new convention put on a
non-trivial parameter if the caller function guarantees to the callee
that the parameter has the deallocating bit set in its object header.

This means that retains and releases do not need to be emitted on these
parameters even though they are non-trivial. This helps to solve a bug
in +0 self and makes it trivial for the optimizer to perform
optimizations based on this property.

It is not emitted yet by SILGen and will only be put on the self
argument of Deallocator functions.

Swift SVN r26179