aarch64 interoperability

[ua1arn]

Few changes need for painless compile Cortex-A53 projects:

and

[JonatanAntoni]

Hi @ua1arn,

looks non impacting any exiting CMSIS-based code.
Please go ahead and raise a pull-request.

Did you check other compilers as well? Perhaps it makes sense to add a similar change to the other compiler, too.

Cheers,
Jonatan

[ua1arn]

Other compilers may have different predefined macro.

[ua1arn]

pull-request too heavy for me ;)