path for gdb/dwarf2read.c, support 16-bit targets in dwarf-2

[Jim Blandy]

> > But which is the correct address --- 0x0000000080000200, or
> >                                      0xffffffff80000200?
> 
> That is target dependant but well defined.
> 
> The MIPS ISA/ABI is carefully defined so MIPS2 on MIPS3 et.al. ensures
> that the upper 32 bits is signextended from the low 32 bits.

Okay --- so if the user actually has the address of that object in a
register, they're going to see 0xffffffff80000200, right?  So doesn't
your change cause GDB to print incorrect addresses?

Based on my experience with the PA 2.0 port, 64-bit addresses are a
genuine pain to handle.  It would be nice to find a comfortable way to
deal with this.  But I don't think having GDB print addresses that are
related, but wrong, is a good idea.