Fix bug that would lead to joining preprocessor directives.

Before: #include "a.h" #include "b.h"
After:  #include "a.h"
        #include "b.h"

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172424 91177308-0d34-0410-b5e6-96231b3b80d8