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/option.h

@@ -1,81 +1,7 @@
 #ifndef NVIM_OPTION_H
 #define NVIM_OPTION_H
 
-#include <stdint.h>
-
-/* option.c */
-void set_init_1(void);
-void set_string_default(char *name, char_u *val);
-void set_number_default(char *name, long val);
-void free_all_options(void);
-void set_init_2(void);
-void set_init_3(void);
-void set_helplang_default(char_u *lang);
-void set_title_defaults(void);
-int do_set(char_u *arg, int opt_flags);
-void set_options_bin(int oldval, int newval, int opt_flags);
-int get_viminfo_parameter(int type);
-char_u *find_viminfo_parameter(int type);
-void check_options(void);
-void check_buf_options(buf_T *buf);
-void free_string_option(char_u *p);
-void clear_string_option(char_u **pp);
-void set_term_option_alloced(char_u **p);
-int was_set_insecurely(char_u *opt, int opt_flags);
-void set_string_option_direct(char_u *name, int opt_idx, char_u *val,
-                                      int opt_flags,
-                                      int set_sid);
-char_u *check_colorcolumn(win_T *wp);
-char_u *check_stl_option(char_u *s);
-int get_option_value(char_u *name, long *numval, char_u **stringval,
-                             int opt_flags);
-int get_option_value_strict(char *name,
-                            int64_t *numval,
-                            char **stringval,
-                            int opt_type,
-                            void *from);
-char_u *option_iter_next(void **option, int opt_type);
-char_u *set_option_value(char_u *name, long number, char_u *string,
-                                 int opt_flags);
-char_u *get_term_code(char_u *tname);
-char_u *get_highlight_default(void);
-char_u *get_encoding_default(void);
-int makeset(FILE *fd, int opt_flags, int local_only);
-int makefoldset(FILE *fd);
-void clear_termoptions(void);
-void free_termoptions(void);
-void free_one_termoption(char_u *var);
-void set_term_defaults(void);
-void comp_col(void);
-void unset_global_local_option(char *name, void *from);
-char_u *get_equalprg(void);
-void win_copy_options(win_T *wp_from, win_T *wp_to);
-void copy_winopt(winopt_T *from, winopt_T *to);
-void check_win_options(win_T *win);
-void check_winopt(winopt_T *wop);
-void clear_winopt(winopt_T *wop);
-void buf_copy_options(buf_T *buf, int flags);
-void reset_modifiable(void);
-void set_iminsert_global(void);
-void set_imsearch_global(void);
-void set_context_in_set_cmd(expand_T *xp, char_u *arg, int opt_flags);
-int ExpandSettings(expand_T *xp, regmatch_T *regmatch, int *num_file,
-                           char_u ***file);
-int ExpandOldSetting(int *num_file, char_u ***file);
-int langmap_adjust_mb(int c);
-int has_format_option(int x);
-int shortmess(int x);
-void vimrc_found(char_u *fname, char_u *envname);
-void change_compatible(int on);
-int option_was_set(char_u *name);
-void reset_option_was_set(char_u *name);
-int can_bs(int what);
-void save_file_ff(buf_T *buf);
-int file_ff_differs(buf_T *buf, int ignore_empty);
-int check_ff_value(char_u *p);
-long get_sw_value(buf_T *buf);
-long get_sts_value(void);
-void find_mps_values(int *initc, int *findc, int *backwards,
-                             int switchit);
-
-#endif /* NVIM_OPTION_H */
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "option.h.generated.h"
+#endif
+#endif  // NVIM_OPTION_H