Fix tagging of DEFUN by etags

Fix tagging of DEFUN by etags

* lib-src/etags.c (C_entries): Tag DEFUN twice: once with its C
name, and then again with its Lisp name.  This restores the
ability to find Lisp primitives by their C name, which was lost
when the etags back-end was switched to a more strict search
criteria.

* test/etags/ETAGS.good_1:
* test/etags/ETAGS.good_2:
* test/etags/ETAGS.good_3:
* test/etags/ETAGS.good_4:
* test/etags/ETAGS.good_5:
* test/etags/ETAGS.good_6:
* test/etags/CTAGS.good: Adapt to the changes in etags.c wrt
tagging DEFUN.