Fix for SNPRINTF test in configure

From: Tom Lane <tgl@sss.pgh.pa.us>

src/configure

@@ -4086,7 +4086,7 @@ EOF
 
 else
   echo "$ac_t""no" 1>&6
-ISINF='snprintf.o'
+SNPRINTF='snprintf.o'
 fi
 
 

src/configure.in

@@ -534,7 +534,7 @@ AC_CHECK_FUNCS(fp_class fp_class_d class)
 AC_CHECK_FUNCS(sigprocmask waitpid setsid fcvt)
 AC_CHECK_FUNC(snprintf,
 	      AC_DEFINE(HAVE_SNPRINTF),
-	      ISINF='snprintf.o')
+	      SNPRINTF='snprintf.o')
 AC_SUBST(SNPRINTF)
 AC_CHECK_FUNC(isinf,
 	      AC_DEFINE(HAVE_ISINF),