Restore linking libpq into pg_ctl on Mingw builds.

Commit 1ae85365 missed this.  Per Andrew Dunstan.

src/bin/pg_ctl/Makefile

@@ -16,12 +16,20 @@ subdir = src/bin/pg_ctl
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
+# On Windows, we need to link with libpq, just for use of pqexpbuffer;
+# but let's not pull that in on platforms where we don't need it.
+ifeq ($(PORTNAME), win32)
+override CPPFLAGS := -I$(libpq_srcdir) $(CPPFLAGS)
+SUBMAKE_LIBPQ := submake-libpq
+LIBPQ_PGPORT := $(libpq_pgport)
+endif
+
 OBJS=	pg_ctl.o $(WIN32RES)
 
 all: pg_ctl
 
-pg_ctl: $(OBJS) | submake-libpgport
-	$(CC) $(CFLAGS) $(OBJS) $(LDFLAGS) $(LDFLAGS_EX) $(LIBS) -o $@$(X)
+pg_ctl: $(OBJS) | submake-libpgport $(SUBMAKE_LIBPQ)
+	$(CC) $(CFLAGS) $(OBJS) $(LIBPQ_PGPORT) $(LDFLAGS) $(LDFLAGS_EX) $(LIBS) -o $@$(X)
 
 install: all installdirs
 	$(INSTALL_PROGRAM) pg_ctl$(X) '$(DESTDIR)$(bindir)/pg_ctl$(X)'