Move our punting mechanisms into a separate header

Summary: Not needed in ir.h, so lets not include them all over them place.

Highly doubt moving the exception constructors will cause a perf
regression.

Reviewed By: @edwinsmith

Differential Revision: D1579698
Remove side-exiting arcs from TransCFG

Summary: Since D1052990 switched slow side exits from doing REQ_INTERP to do
actual InterpOnes, arcs due to slow side exits started to be inserted
in the TransCFG.  The hottrace region selector had logic to avoid
following these arcs when forming a region, and wholecfg would need
something similar.  Instead of replicating that logic in wholecfg,
this diff prevents the insertion of such arcs in TransCFG altogether.

This issue was caught by the region checker running wholecfg in perflab.

Reviewed By: @bertmaher

Differential Revision: D1578852