* keep coherent SP/PC in gobuf
	  (i.e., SP that would be in use at that PC)
	* gogocall replaces setspgoto,
	  should work better in presence of link registers
	* delete unused system calls

only amd64; 386 is now broken

R=r
DELTA=548  (183 added, 183 deleted, 182 changed)
OCL=30381
CL=30442