Add CortexM::is_vector_catch
Add CortexM::is_vector_catch

Will be useful for special handling of SIGSEGV etc arising from
exceptions.

mesheven/pyOCD,pyocd/pyOCD,mbedmicro/pyOCD,mesheven/pyOCD,flit/pyOCD,mesheven/pyOCD,flit/pyOCD,mbedmicro/pyOCD,mbedmicro/pyOCD,pyocd/pyOCD