[C++11] Simplify some loops in Sema::CorrectTypo as range-based for loops.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204524 91177308-0d34-0410-b5e6-96231b3b80d8
Be a bit smarter about what nested name qualifiers to allow when
performing typo correction on very short (1 or 2 char) identifiers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204525 91177308-0d34-0410-b5e6-96231b3b80d8