Add a 'count' field to the DWARF subrange.

Add a 'count' field to the DWARF subrange.

The count field is necessary because there isn't a difference between the 'lo'
and 'hi' attributes for a one-element array and a zero-element array. When the
count is '0', we know that this is a zero-element array. When it's >=1, then
it's a normal constant sized array. When it's -1, then the array is unbounded.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169219 91177308-0d34-0410-b5e6-96231b3b80d8