usr/src/uts/sun4/ml/offsets.in should provide a define for proc_t->p_agenttp.
this change only affects the dynamic generation of the assym.h which are
never shipped and are only used while compiling the kernel. (So this change
should have no impact on deliverable bits.) This is needed for the brandz
framework to be able to detect the presence of agent lwps. It's worth
mentioning that the offsets.in file on x86 already provides access to
this field.