Patch by Chris Wailes <chris.wailes@gmail.com>.
Reviewed by delesley, dblaikie.

Add the annotations and code needed to support a basic 'consumed' analysis.

Summary:
This new analysis is based on academic literature on linear types.  It tracks
the state of a value, either as unconsumed, consumed, or unknown.  Methods are
then annotated as CallableWhenUnconsumed, and when an annotated method is
called while the value is in the 'consumed' state a warning is issued.  A value
may be tested in the conditional statement of an if-statement; when this occurs
we know the state of the value in the different branches, and this information
is added to our analysis.  The code is still highly experimental, and the names
of annotations or the algorithm may be subject to change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188206 91177308-0d34-0410-b5e6-96231b3b80d8