Report source location of returns_nonnull attribute in UBSan reports.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217400 91177308-0d34-0410-b5e6-96231b3b80d8
Fix PCHs that import more than one module

We were passing < to std::unique, but it expects ==. Since the input is
sorted, we were always trimming it to one entry.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217402 91177308-0d34-0410-b5e6-96231b3b80d8