synology_armv5: add extra_cc NO_PTHREAD_STACKSIZE

- this removes weired warning "pthread_attr_setstacksize() failed in start_thread with error 22 Invalid argument" from oscam log
- see https://board.streamboard.tv/forum/thread/48195-gel%C3%B6st-ds212plus-oscam-v11718-https-trac-streamboard-tv-oscam-ticket-4277/

support/toolchains.cfg/synology_armv5

@@ -1,7 +1,7 @@
 _toolchainname="synology_armv5";
 default_use="USE_UTF8 USE_LIBCRYPTO";
 extra_use="";
-extra_cc="";
+extra_cc="-DNO_PTHREAD_STACKSIZE";
 extra_ld="";
 _description="Synology Marvell 628x devices, Synology DS112x";
 _oscamconfdir_default="/etc/tuxbox/config";