Include isinf.o in libecpg if isinf() is not available on the system.

Patch done by Jiang Guiqing <jianggq@cn.fujitsu.com>.

src/interfaces/ecpg/ecpglib/Makefile

@@ -26,7 +26,7 @@ LIBS := $(filter-out -lpgport, $(LIBS))
 
 OBJS= execute.o typename.o descriptor.o sqlda.o data.o error.o prepare.o memory.o \
 	connect.o misc.o path.o pgstrcasecmp.o \
-	$(filter snprintf.o strlcpy.o win32setlocale.o, $(LIBOBJS))
+	$(filter snprintf.o strlcpy.o win32setlocale.o isinf.o, $(LIBOBJS))
 
 # thread.c is needed only for non-WIN32 implementation of path.c
 ifneq ($(PORTNAME), win32)
@@ -57,7 +57,7 @@ include $(top_srcdir)/src/Makefile.shlib
 # necessarily use the same object files as the backend uses. Instead,
 # symlink the source files in here and build our own object file.
 
-path.c pgstrcasecmp.c snprintf.c strlcpy.c thread.c win32setlocale.c: % : $(top_srcdir)/src/port/%
+path.c pgstrcasecmp.c snprintf.c strlcpy.c thread.c win32setlocale.c isinf.c: % : $(top_srcdir)/src/port/%
 	rm -f $@ && $(LN_S) $< .
 
 misc.o: misc.c $(top_builddir)/src/port/pg_config_paths.h