Update mbed_stats.c to use __ARMCC_VERSION flag to be compatible with AC6
Update mbed_stats.c to use __ARMCC_VERSION flag to be compatible with AC6

andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,kjbracey-arm/mbed,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed