Updates for GCC 4.5.3

* Include correct GCC headers depending upon version
* GCC does not stop the watchdog, so do it in PlatformP.nc
* Stopping watchdog in MotePlatformC no longer needed (olimexp16,
  tmicore, tmirws)
* tmicore writes TxIV in MoteClockP so needs MSP430REG_NORACE()