Bug#14862 undefined reference to `isinf' on SOLARIS - strings/strtod.c

- Rely only on HAVE_ISINF to determine if 'isinf' can be used.

include/my_global.h

@@ -812,7 +812,12 @@ typedef SOCKET_SIZE_TYPE size_socket;
 #define SSIZE_MAX ((~((size_t) 0)) / 2)
 #endif
 
-#if !defined(HAVE_ISINF) && !defined(isinf)
+#if !defined(HAVE_ISINF)
+/* The configure check for "isinf with math.h" has failed */
+#ifdef isinf
+#undef isinf
+#endif
+/* Define isinf to never say that X is infinite */
 #define isinf(X)    0
 #endif