Add a new warning to -Wloop-analysis to detect suspicious increments or
decrements inside for loops.  Idea for this warning proposed in PR15636:

http://llvm.org/bugs/show_bug.cgi?id=15636


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187817 91177308-0d34-0410-b5e6-96231b3b80d8