pp.c:pp_complement: No PUTBACK necessary

We don’t manipulate the stack pointer here.
pp.c:pp_i_negate: No PUTBACK necessary

We don’t manipulate the stack pointer here.
pp.c:pp_sin: Less stack fiddling

No need to pop and push.  No need to extend the stack.  No need for
PUTBACK with those changes, as we no longer maniputale the stack
pointer (and even when we did it always ended up with the same value).
pp.c:pp_int: No need for PUTBACK

We don’t manipulate the stack pointer at all here.
pp.c:pp_negate: No PUTBACK necessary

We don’t manipulate the stack pointer here.