.gnu.linkonce COFF support

[DJ Delorie]

> The long section name support is different and unrelated.  As far as I
> know, the binutils support long section names as they are used and
> generated by the Microsoft tools.

There are two ways of implementing long section names in COFF: the gnu
way, and the PE way.  We got that wrong too.  The GNU way is to store
the name in the string table.  The PE way is to use multiple auxents.
As far as *using* long section names for various features, that's OK
with me, except for the COMDAT thing.

Not, of course, that I care about what MS's format says, since djgpp
is independent of PE, but I'd hate to see us do the work twice if we
can do it once for both platforms.