Fixes handling of empty lines in macros.

Now correctly formats:
 #define A \
   \
   b;
to
 #define A b;

Added the state whether an unwrapped line is a macro to the debug
output.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174878 91177308-0d34-0410-b5e6-96231b3b80d8