cpu/native: define default CLOCK_CORECLOCK constant

cpu/native/include/periph_conf.h

@@ -16,10 +16,21 @@
 #ifndef PERIPH_CONF_H
 #define PERIPH_CONF_H
 
+#include "macros/units.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/**
+ * @brief   System core clock in Hz
+ *
+ *  1GHz is an arbitrary value used for compatibility with other platforms.
+ */
+#ifndef CLOCK_CORECLOCK
+#define CLOCK_CORECLOCK     GHZ(1)
+#endif
+
 /**
  * @name hardware timer clock skew avoidance
  * @{