isinf and isnan are macros, not functions; fix configure script
to use AC_CHECK_DECLS instead of AC_CHECK_FUNCS for these.
(See discussion in issue #4506)
diff --git a/PC/pyconfig.h b/PC/pyconfig.h
index d287401..255554a 100644
--- a/PC/pyconfig.h
+++ b/PC/pyconfig.h
@@ -399,11 +399,11 @@
/* Define to 1 if you have the `copysign' function. */
#define HAVE_COPYSIGN 1
-/* Define to 1 if you have the `isinf' function. */
-#define HAVE_ISINF 1
+/* Define to 1 if you have the `isinf' macro. */
+#define HAVE_DECL_ISINF 1
/* Define to 1 if you have the `isnan' function. */
-#define HAVE_ISNAN 1
+#define HAVE_DECL_ISNAN 1
/* Define if on AIX 3.
System headers sometimes define this.