Convert definitions to standard C.

Convert definitions to standard C.

* src/strftime.c (LOCALE_PARAM_DECL): Update for standard C.
(LOCALE_PARAM, LOCALE_PARAM_PROTO): Remove, unused.
(memcpy_lowcase, so_week_days, extra_args_spec, emacs_strftimeu):
Convert definitions to standard C.
* src/regex.c: Do not include <stdlib.h>, config.h does it.
Include unistd.h.
(xrealloc, init_syntax_once, re_match, regcomp, regexec)
(regerror, regfree): Convert definitions to standard C.
* src/mktime.c (my_mktime_localtime_r, ydhms_tm_diff, ranged_convert)
(__mktime_internal): Convert definitions to standard C.