Write 64-bit address in DWARF if we are on 64-bit architecture.

DWARF includes code address.  Make sure they are of the right size.

I have kept them as 32-bit until now to keep consistent with the
old code.  I do not think that having 32-bit addresses was an issue
since we were using 32-bit Elf, but since we plan to switch to
64-bit Elf, we should definitely be using 64-bit address.

Change-Id: I57138c0dda2d37fc6f0f9329b31d61f38a2d6fcb