Assume macros to contain declarations.

This seems to be the vastly more common case. If we find enough
examples to the contrary, we can make it smarter.

Before: #define MACRO void f(int * a)
After:  #define MACRO void f(int *a)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181687 91177308-0d34-0410-b5e6-96231b3b80d8