for Ubuntu

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@105338 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/cstddef b/include/cstddef
index 11d07a2..f6b34ad 100644
--- a/include/cstddef
+++ b/include/cstddef
@@ -34,6 +34,13 @@
 */
 
 #include <__config>
+
+#ifdef __GLIBC__
+#define __need_NULL
+#define __need_ptrdiff_t
+#define __need_size_t
+#endif
+
 #include <stddef.h>
 
 #pragma GCC system_header