rtl problem when processing arm thumb mode switch

[Chris Johns]

Peng Fan wrote:
> I think if the rap file is compiled in thumb, this size of the rap file
> will be reduced.

The smaller code size can benefit the base image because small code size 
reduces cache pressure and can improve performance.

> So i want to introduce it. If this is not needed, it would be easy to
> just handle arm to arm and thumb to thumb call.

If a use case comes up and it makes sense we can consider it then.

Chris