/* uses PUSHs, so SP must be at start, PUSHs sv on Perl stack, then returns from
xsub; this is a little more machine code/tailcall friendly than mPUSHs(foo);
/* uses PUSHs, so SP must be at start, PUSHs sv on Perl stack, then returns from
xsub; this is a little more machine code/tailcall friendly than mPUSHs(foo);