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/ex_cmds.h

@@ -1,75 +1,7 @@
 #ifndef NVIM_EX_CMDS_H
 #define NVIM_EX_CMDS_H
-/* ex_cmds.c */
 
-void do_ascii(exarg_T *eap);
-void ex_align(exarg_T *eap);
-void ex_sort(exarg_T *eap);
-void ex_retab(exarg_T *eap);
-int do_move(linenr_T line1, linenr_T line2, linenr_T dest);
-void ex_copy(linenr_T line1, linenr_T line2, linenr_T n);
-void free_prev_shellcmd(void);
-void do_bang(int addr_count, exarg_T *eap, int forceit, int do_in,
-                     int do_out);
-void do_shell(char_u *cmd, int flags);
-char_u *make_filter_cmd(char_u *cmd, char_u *itmp, char_u *otmp);
-void append_redir(char_u *buf, int buflen, char_u *opt, char_u *fname);
-int viminfo_error(char *errnum, char *message, char_u *line);
-int read_viminfo(char_u *file, int flags);
-void write_viminfo(char_u *file, int forceit);
-int viminfo_readline(vir_T *virp);
-char_u *viminfo_readstring(vir_T *virp, int off, int convert);
-void viminfo_writestring(FILE *fd, char_u *p);
-void do_fixdel(exarg_T *eap);
-void print_line_no_prefix(linenr_T lnum, int use_number, int list);
-void print_line(linenr_T lnum, int use_number, int list);
-int rename_buffer(char_u *new_fname);
-void ex_file(exarg_T *eap);
-void ex_update(exarg_T *eap);
-void ex_write(exarg_T *eap);
-int do_write(exarg_T *eap);
-int check_overwrite(exarg_T *eap, buf_T *buf, char_u *fname, char_u *
-                            ffname,
-                            int other);
-void ex_wnext(exarg_T *eap);
-void do_wqall(exarg_T *eap);
-int not_writing(void);
-int getfile(int fnum, char_u *ffname, char_u *sfname, int setpm,
-                    linenr_T lnum,
-                    int forceit);
-int do_ecmd(int fnum, char_u *ffname, char_u *sfname, exarg_T *eap,
-                    linenr_T newlnum, int flags,
-                    win_T *oldwin);
-void ex_append(exarg_T *eap);
-void ex_change(exarg_T *eap);
-void ex_z(exarg_T *eap);
-int check_restricted(void);
-int check_secure(void);
-void do_sub(exarg_T *eap);
-int do_sub_msg(int count_only);
-void ex_global(exarg_T *eap);
-void global_exe(char_u *cmd);
-int read_viminfo_sub_string(vir_T *virp, int force);
-void write_viminfo_sub_string(FILE *fp);
-void free_old_sub(void);
-int prepare_tagpreview(int undo_sync);
-void ex_help(exarg_T *eap);
-char_u *check_help_lang(char_u *arg);
-int help_heuristic(char_u *matched_string, int offset, int wrong_case);
-int find_help_tags(char_u *arg, int *num_matches, char_u ***matches,
-                           int keep_lang);
-void fix_help_buffer(void);
-void ex_exusage(exarg_T *eap);
-void ex_viusage(exarg_T *eap);
-void ex_helptags(exarg_T *eap);
-void ex_sign(exarg_T *eap);
-int sign_get_attr(int typenr, int line);
-char_u *sign_get_text(int typenr);
-void *sign_get_image(int typenr);
-char_u *sign_typenr2name(int typenr);
-void free_signs(void);
-char_u *get_sign_name(expand_T *xp, int idx);
-void set_context_in_sign_cmd(expand_T *xp, char_u *arg);
-void ex_drop(exarg_T *eap);
-
-#endif /* NVIM_EX_CMDS_H */
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "ex_cmds.h.generated.h"
+#endif
+#endif  // NVIM_EX_CMDS_H