[attributes] Extend os_returns_(not_?)_retained attributes to parameters

When applied to out-parameters, the attributes specify the expected lifetime of the written-into object.

Additionally, introduce OSReturnsRetainedOn(Non)Zero attributes, which
specify that an ownership transfer happens depending on a return code.

Differential Revision: https://reviews.llvm.org/D56292

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@350942 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed