Fix Makefile problem which prevented installation on VPATH builds.

src/interfaces/ecpg/include/Makefile

@@ -7,19 +7,21 @@ override CPPFLAGS := -DFRONTEND \
 	-I$(libpq_srcdir) -I$(top_builddir)/src/port $(CPPFLAGS)
 
 informix_esql_dir = $(pkgincludedir)/informix/esql
+ecpg_config_h = $(top_builddir)/src/interfaces/ecpg/include/ecpg_config.h
 
-all: $(top_builddir)/src/interfaces/ecpg/include/ecpg_config.h 
+all: $(ecpg_config_h)
 
 install: all installdirs install-headers
 
 .PHONY: install-headers
-ecpg_headers = ecpgerrno.h ecpglib.h ecpgtype.h sqlca.h sql3types.h ecpg_informix.h ecpg_config.h \
+ecpg_headers = ecpgerrno.h ecpglib.h ecpgtype.h sqlca.h sql3types.h ecpg_informix.h \
 	pgtypes_error.h pgtypes_numeric.h pgtypes_timestamp.h pgtypes_date.h pgtypes_interval.h
 informix_headers = datetime.h decimal.h sqltypes.h sqlda.h
 
 install-headers: $(ecpg_headers) $(informix_headers)
 	for i in $(ecpg_headers); do $(INSTALL_DATA) $(srcdir)/$$i '$(DESTDIR)$(includedir)' || exit; done
 	for i in $(informix_headers); do $(INSTALL_DATA) $(srcdir)/$$i '$(DESTDIR)$(informix_esql_dir)' || exit; done
+	$(INSTALL_DATA) $(ecpg_config_h) '$(DESTDIR)$(includedir)'
 
 installdirs:
 	$(mkinstalldirs) '$(DESTDIR)$(includedir)' '$(DESTDIR)$(informix_esql_dir)'