Don't use std::next() on an input iterator; NFC.

Instead, advance the old-fashioned way, as std::next() cannot be used on an input iterator until C++17.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@346266 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed