Also align trailing line comments in include directives.

Before:
  #include <a> // for x
  #include <a/b/c> // for yz
After:
  #include <a>     // for x
  #include <a/b/c> // for yz

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172799 91177308-0d34-0410-b5e6-96231b3b80d8