Fix a pretty big but subtle bug counting the number of newlines to emit.

This would cause us to emit different code (in -E mode) for these two files:

---
#define t(x) x

t(a
3)
---
#define t(x) x
t(a
3)
---

In one case, -E would print "a\n3", in the other it printed "a3".  Now
it prints "a3" for both.

This is part of PR1848.

llvm-svn: 44742