Begin the transition to using the AttributesImpl object for the Attributes ivar.

Begin the transition to using the AttributesImpl object for the Attributes ivar.

Start using the AttributesImpl object to hold the value of the attributes. All
queries go through the interfaces now.

This has one unfortunate consequence. I needed to move the AttributesImpl.h file
into include/llvm. But this is only temporary! Otherwise, the changes needed to
support this would be too large.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165433 91177308-0d34-0410-b5e6-96231b3b80d8