Use the incremental parser's source location offsets in the LookupHelper, too.

This would give us proper ordering of the source locations, useful when clang
wants to compare them.
Remove redundant vars.
Update llvm because of vital fixes in the pretty printer.
Use the new interface, instead.
Pass in a includer's source location so clang can compare source locations.

This fixes a long standing issue with a clang assert when comparing with a
location coming from the lookup helper.
Simple test for Standard Library headers, and a few more workarounds
Bypass anonymous enum typedefs and functions with trailing return types
Incorporating DeclPrinter fix for parameter packs into cling
Merge branch 'cling-new-llvm' of github.com:manasij7479/cling into cling-new-llvm