Add automatic generation of headers

- The 'stripdecls.py' script replaces declarations in all headers by includes to
  generated headers.
  `ag '#\s*if(?!ndef NEOVIM_).*((?!#\s*endif).*\n)*#ifdef INCLUDE_GENERATED'`
  was used for this.
- Add and integrate gendeclarations.lua into the build system to generate the
  required includes.
- Add -Wno-unused-function
- Made a bunch of old-style definitions ANSI

This adds a requirement: all type and structure definitions must be present
before INCLUDE_GENERATED_DECLARATIONS-protected include.

Warning: mch_expandpath (path.h.generated.h) was moved manually. So far it is
the only exception.

src/nvim/fileio.h

@@ -17,76 +17,7 @@ typedef struct {
   char_u      *globaldir;       /* saved value of globaldir */
 } aco_save_T;
 
-/* fileio.c */
-void filemess(buf_T *buf, char_u *name, char_u *s, int attr);
-int readfile(char_u *fname, char_u *sfname, linenr_T from,
-             linenr_T lines_to_skip, linenr_T lines_to_read, exarg_T *eap,
-             int flags);
-void prep_exarg(exarg_T *eap, buf_T *buf);
-void set_file_options(int set_options, exarg_T *eap);
-void set_forced_fenc(exarg_T *eap);
-int buf_write(buf_T *buf, char_u *fname, char_u *sfname, linenr_T start,
-              linenr_T end, exarg_T *eap, int append, int forceit,
-              int reset_changed,
-              int filtering);
-void msg_add_fname(buf_T *buf, char_u *fname);
-void msg_add_lines(int insert_space, long lnum, off_t nchars);
-void shorten_fnames(int force);
-char_u *modname(char_u *fname, char_u *ext, int prepend_dot);
-int vim_fgets(char_u *buf, int size, FILE *fp);
-int tag_fgets(char_u *buf, int size, FILE *fp);
-int vim_rename(char_u *from, char_u *to);
-int check_timestamps(int focus);
-int buf_check_timestamp(buf_T *buf, int focus);
-void buf_reload(buf_T *buf, int orig_mode);
-void buf_store_file_info(buf_T *buf, FileInfo *file_info);
-void write_lnum_adjust(linenr_T offset);
-void vim_deltempdir(void);
-char_u *vim_tempname(int extra_char);
-void forward_slash(char_u *fname);
-void aubuflocal_remove(buf_T *buf);
-int au_has_group(char_u *name);
-void do_augroup(char_u *arg, int del_group);
-void free_all_autocmds(void);
-int check_ei(void);
-char_u *au_event_disable(char *what);
-void au_event_restore(char_u *old_ei);
-void do_autocmd(char_u *arg, int forceit);
-int do_doautocmd(char_u *arg, int do_msg);
-void ex_doautoall(exarg_T *eap);
-int check_nomodeline(char_u **argp);
-void aucmd_prepbuf(aco_save_T *aco, buf_T *buf);
-void aucmd_restbuf(aco_save_T *aco);
-int apply_autocmds(event_T event, char_u *fname, char_u *fname_io,
-                   int force,
-                   buf_T *buf);
-int apply_autocmds_retval(event_T event, char_u *fname, char_u *fname_io,
-                          int force, buf_T *buf,
-                          int *retval);
-int has_cursorhold(void);
-int trigger_cursorhold(void);
-int has_cursormoved(void);
-int has_cursormovedI(void);
-int has_textchanged(void);
-int has_textchangedI(void);
-int has_insertcharpre(void);
-void block_autocmds(void);
-void unblock_autocmds(void);
-char_u *getnextac(int c, void *cookie, int indent);
-int has_autocmd(event_T event, char_u *sfname, buf_T *buf);
-char_u *get_augroup_name(expand_T *xp, int idx);
-char_u *set_context_in_autocmd(expand_T *xp, char_u *arg, int doautocmd);
-char_u *get_event_name(expand_T *xp, int idx);
-int autocmd_supported(char_u *name);
-int au_exists(char_u *arg);
-int match_file_pat(char_u *pattern, regprog_T *prog, char_u *fname,
-                   char_u *sfname, char_u *tail,
-                   int allow_dirs);
-int match_file_list(char_u *list, char_u *sfname, char_u *ffname);
-char_u *file_pat_to_reg_pat(char_u *pat, char_u *pat_end,
-                            char *allow_dirs,
-                            int no_bslash);
-long read_eintr(int fd, void *buf, size_t bufsize);
-long write_eintr(int fd, void *buf, size_t bufsize);
-
-#endif /* NVIM_FILEIO_H */
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "fileio.h.generated.h"
+#endif
+#endif  // NVIM_FILEIO_H