add ptrdiff_t to acconfig.h

diff --git a/acconfig.h b/acconfig.h
index a194cbf787da6b74af56a9d31b337a5206f393db..b3414010ec39152ab832a0624b101e9db711ba76 100644 (file)
--- a/acconfig.h
+++ b/acconfig.h
@@ -69,3 +69,6 @@
 /* Do we have proper memory information in struct sysinfo */
 #undef MEMINFO_IN_SYSINFO
 
+/* Define the ptrdiff_t type if your system doesn't have it */
+#undef ptrdiff_t
+