Introduce MG_ENABLE_CUSTOM_MILLIS

mongoose.c

@@ -4766,6 +4766,8 @@ int mg_check_ip_acl(struct mg_str acl, uint32_t remote_ip) {
   return allowed == '+';
 }
 
+#if MG_ENABLE_CUSTOM_MILLIS
+#else
 int64_t mg_millis(void) {
 #if MG_ARCH == MG_ARCH_WIN32
   return GetTickCount();
@@ -4800,6 +4802,7 @@ int64_t mg_millis(void) {
   return time(NULL) * 1000;
 #endif
 }
+#endif
 
 #ifdef MG_ENABLE_LINES
 #line 1 "src/ws.c"