This is the first step towards handling preprocessor directives. This
patch only fixes the most pressing issue, namely correctly escaping
newlines for tokens within a sequence of a preprocessor directive.

The next step will be to fix incorrect format decisions on #define
directives.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171393 91177308-0d34-0410-b5e6-96231b3b80d8