[llvm-dwarfdump] - Change format for .gdb_index dump.

It is useful to output size of ranges when address ranges
section of .gdb_index is dumped.

It helps to compare outputs produced by different linkers,
for example. In that case address ranges can look very different,
when they are the same at fact. Difference comes from different 
low address because of different address of .text.

Differential revision: https://reviews.llvm.org/D32492

llvm-svn: 301527