more buildfarm breakage

mingw is unhappy with my latest stab at fixing the mess created by the
errcodes patch last night.  It appears that there are several files in
src/port that include "postgres.h" even when FRONTEND is defined.  For
example, chklocale.c does this, which looks good:

#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

But dirent.c, pipe.c, and win32error.c just do this, which seems ungood:

#include "postgres.h"

Can we get away with using the former incantation for these files, or
do they really need to include the backend version of that file even
when compiled with -DFRONTEND?  If so, I can fix it by adding some
more dependencies, but I thought I'd ask first.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company