Dependent Address Space Support

This patch relates to: https://reviews.llvm.org/D33666 This adds support
for template parameters to be passed to the address_space attribute. 
The main goal is to add further flexibility to the attribute and allow 
for it to be used easily with templates.

The main additions are a new type (DependentAddressSpaceType) alongside 
its TypeLoc and its mangling. As well as the logic required to support 
dependent address spaces which mainly resides in TreeTransform.h and 
SemaType.cpp.

llvm-svn: 314649