Simpler abbrev parsing using less memory

[Mark Wielaard]

On Tue, Dec 26, 2017 at 08:38:38PM +0100, Mark Wielaard wrote:
> [PATCH 1/2] libdw: New get_uleb128_unchecked to use with already
>                    checked Dwarf_Abbrev.
> 
> So the first patch introduces a get_uleb128_unchecked function that
> is used for re-reading such uleb128 values.
> 
> The second patch reduces the size of the struct Dwarf_Abbrev by not
> storing the attrcnt and by using bitfields for has_children and code.
> 
> [PATCH 2/2] libdw: Reduce size of struct Dwarf_Abbrev.

I pushed both patches to master.