bug#25280: 25.1; define-inline doesn't support &rest

[Leo Liu]

inline.el has a comment FIXME: How can this work with CL arglists? but
it is worse. it doesn't support &rest.

Try compile the following example:

  (define-inline rest (&rest xs)
    (inline-quote (apply #'vector ,xs)))
  
  (princ (rest 1 2))

In toplevel form:
test.el:7:1:Warning: ‘1’ is a malformed function

The header comment says defsubst: not as efficient. Could this be made
clearer? In what way is defsubst less efficient?

What is the outlook for defsubst or cl-defsubst? Are they on their way
out? 

Thanks,
Leo