Tune UNEVALLED functions by using XCAR instead of Fcar, etc.

Tune UNEVALLED functions by using XCAR instead of Fcar, etc.

* data.c (Fsetq_default):
* eval.c (Fif, Fcond, Fprog1, Fsetq, Fquote, Ffunction, Fdefvar)
(Fdefconst, FletX, Flet, Fwhile, Fcatch, Funwind_protect)
(Fcondition_case):
Tune by taking advantage of the fact that ARGS is always a list
when a function is declared to have UNEVALLED args.