sysclk: make dvfs work

Source/sys-clk/common/include/memmem.h

@@ -0,0 +1,17 @@
+#ifndef MEMMEM_IMPL_H
+#define MEMMEM_IMPL_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void *memmem_impl(void *haystack, size_t haystacklen,
+                  const void *needle, size_t needlelen);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif