Patch to make top-of-tree GDB compile on Digital UNIX

[Guy Harris]

> Elena also noted that the patch combined two very different changes. 

If you're referring to her comment

	Your changes to symbol_add_stub are actually more than what
	necessary for compilation.  You have added the use of the
	function build_section_addr_info_from_section_table() which
	Kevin Buettner introduced for other purposes a few weeks back. 

it was, at least as I was constructing it, only one change, as I'd
inferred, perhaps incorrectly, from other changes that the changes to
use "build_section_addr_info_from_section_table()" *were* the way to fix
the compilation problem; they weren't an attempt on my part to
experimentally clean the code up.

I don't particularly care how it's fixed, as long as it compiles and
works; if the changes Elena suggested are sufficient to get it to build
and work, you might as well go with those.