Ensure the CORTEX_M0_STM32F0518_IAR demo builds after updates to the Cortex-M0 port...

Ensure the CORTEX_M0_STM32F0518_IAR demo builds after updates to the Cortex-M0 port layer - required an update to the project settings to allow IAR extensions as the port layer now uses the _weak qualifier.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2783 1d2547de-c912-0410-9cb9-b8ca96c0e9e2