narwhal and PGDLLIMPORT

I happened to notice today that the owner of buildfarm member narwhal
is trying to revive it after a long time offline, but it's failing in
the 9.3 branch (and not attempting to build HEAD, yet).  The cause
appears to be that contrib/postgres_fdw is referencing the DateStyle
and IntervalStyle variables, which aren't marked PGDLLIMPORT.
Hm, well, that would be an easy change ... but that code was committed
last March.  How is it that we didn't notice this long ago?

What this seems to indicate is that narwhal is the only buildfarm
animal that has a need for PGDLLIMPORT marks on global variables that
are referenced by extensions.  Furthermore, nobody has attempted to
build 9.3 on a platform that needs that (or at least they've not
reported failure to us).

According to the buildfarm database, narwhal is running a gcc build on
Windows 2003.  That hardly seems like a mainstream use case.  I could
believe that it might be of interest to developers, but clearly no
developers are actually running such a build.

I think we should give serious consideration to desupporting this
combination so that we can get rid of the plague of PGDLLIMPORT
marks.  Obviously this would depend on confirming that there are
no more-interesting Windows build methods that require it --- but
if there are any, I'd sure demand that there be an active buildfarm
instance to keep us from breaking the case again in future.

Thoughts?
        regards, tom lane