system: BTime: add btime_getpast()

system/BTime.h

@@ -89,7 +89,7 @@ static void BTime_Init (void)
     #endif
 }
 
-static btime_t btime_gettime ()
+static btime_t btime_gettime (void)
 {
     ASSERT(btime_global.initialized)
     
@@ -134,4 +134,9 @@ static btime_t btime_add (btime_t t1, btime_t t2)
     return sum;
 }
 
+static btime_t btime_getpast (void)
+{
+    return INT64_MIN;
+}
+
 #endif