Add the loop end location to the loop metadata. This additional information

Add the loop end location to the loop metadata. This additional information
can be used to improve the locations when generating remarks for loops.

Depends on the companion LLVM change r286227.

Patch by Florian Hahn.

Differential Revision: https://reviews.llvm.org/D25764

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@286456 91177308-0d34-0410-b5e6-96231b3b80d8