stub to enable compilation on macOS,

memory info for macOS is currently not available.

src/frontend/com_sysinfo.c

@@ -386,7 +386,13 @@ static void set_static_system_info(void)
     return;
 } /* end of function set_static_system_info */
 
-
+#elif defined(__APPLE__) && defined(__MACH__)
+/* Get memory information */
+static int get_sysmem(struct sys_memory *memall)
+{
+    fprintf(stderr, "System memory info is not available\n");
+    return -1;
+}
 
 #elif defined(_WIN32)