Introduce getCorrespondingUnsignedType() in TargetInfo to work like the
corresponding AST context function, only restricted to basic integer
types. Use this to ensure getUIntPtrType() gives types consistent with
getIntPtrType(). Fix NVPTX backend to give signed intptr_t.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212982 91177308-0d34-0410-b5e6-96231b3b80d8