libc: Introduce files from SCC

Taken from http://git.simple-cc.org/scc/ from the following commit:

67508ad14af314cea2229783d3c084f28c41daf0

Permission has been granted from the author to use them under the
license BSD-3-Clause instead of ISC.

Change-Id: I65c0ce3ab60c49d34a57533af12a74bd7bde88e5
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/include/lib/libc/stddef.h b/include/lib/libc/stddef.h
new file mode 100644
index 0000000..1150650
--- /dev/null
+++ b/include/lib/libc/stddef.h
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2012-2017 Roberto E. Vargas Caballero
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _STDDEF_H
+#define _STDDEF_H
+
+#include <arch/stddef.h>
+
+#ifndef NULL
+#define NULL ((void *) 0)
+#endif
+
+#define offsetof(st, m) ((size_t)&(((st *)0)->m))
+
+#endif