Hi all,

fifth patch of the series adding support for PACBTI for Cortex-M.

As all the bits in the 'core' field of 'arm_feature_set' struct are
in use this adding a third element to it and is updating the accessor
macros we have.  This is in order to support the following patch that 
adds "-march=armv8.1-m.main+pacbti" flag.

Regards

  Andrea