hideif.el: Support C99 and GNU style variadic macros

hideif.el: Support C99 and GNU style variadic macros

* lisp/progmodes/hideif.el (hif-end-of-line, hif-cpp-prefix)
(hif-ifx-regexp, hif-macro-expr-prefix-regexp, hif-white-regexp)
(hif-macroref-regexp, hif-tokenize, hif-find-any-ifX)
(hif-find-next-relevant, hif-find-previous-relevant, hif-find-range)
(hif-parse-macro-arglist, hif-add-new-defines, hide-ifdef-guts):
Variadic macro parsing, comments and multi-line parsing.
(hif-line-concat, hif-etc-regexp): New regexp for better macro scans.
(hif-expand-token-list, hif-get-argument-list, hif-delimit)
(hif-macro-supply-arguments, hif-canonicalize, hif-find-define):
Variadic macro argument replacement and expansion.
(hif-display-macro): Display variadic macros.
(hif-is-in-comment, hif-search-ifX-regexp): New functions to better
handle macros in comments and comments in macros.