Fix MSVC 2015 compilation failure around range-for without curly braces

It doesn't appear to like this pattern:
  for (auto X : Xs)
    if (...) { ... }
    else ...;

We have heard anecdotes that range based for loops are implemented as a
token rewrite in MSVC's lexer, and that the most challenging part of the
rewrite is finding the end of the for loop. That makes sense, given that
it's a lexer.

llvm-svn: 276315