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/path.h

@@ -14,62 +14,7 @@ typedef enum file_comparison {
   kEqualFileNames = 7     ///< Both don't exist and file names are same.
 } FileComparison;
 
-FileComparison path_full_compare(char_u *s1, char_u *s2, int checkname);
-
-char_u *path_tail(char_u *fname);
-
-char_u *path_tail_with_sep(char_u *fname);
-
-char_u *path_next_component(char_u *fname);
-
-int vim_ispathsep(int c);
-int vim_ispathsep_nocolon(int c);
-int vim_ispathlistsep(int c);
-void shorten_dir(char_u *str);
-int dir_of_file_exists(char_u *fname);
-int vim_fnamecmp(char_u *x, char_u *y);
-int vim_fnamencmp(char_u *x, char_u *y, size_t len);
-char_u *concat_fnames(char_u *fname1, char_u *fname2, int sep)
-  FUNC_ATTR_NONNULL_RET;
-int unix_expandpath(garray_T *gap, char_u *path, int wildoff, int flags,
-                    int didstar);
-int gen_expand_wildcards(int num_pat, char_u **pat, int *num_file,
-                         char_u ***file,
-                         int flags);
-void addfile(garray_T *gap, char_u *f, int flags);
-char_u *get_past_head(char_u *path);
-char_u *concat_str(char_u *str1, char_u *str2) FUNC_ATTR_NONNULL_RET;
-void add_pathsep(char_u *p);
-char_u *FullName_save(char_u *fname, int force);
-void simplify_filename(char_u *filename);
-char_u *find_file_name_in_path(char_u *ptr, int len, int options,
-                               long count,
-                               char_u *rel_fname);
-int path_is_url(char_u *p);
-int path_with_url(char_u *fname);
-int vim_isAbsName(char_u *name);
-int vim_FullName(char_u *fname, char_u *buf, int len, int force);
-char_u *fix_fname(char_u *fname);
-int after_pathsep(char_u *b, char_u *p);
-int same_directory(char_u *f1, char_u *f2);
-int pathcmp(const char *p, const char *q, int maxlen);
-int mch_expandpath(garray_T *gap, char_u *path, int flags);
-
-char_u *path_shorten_fname_if_possible(char_u *full_path);
-
-char_u *path_shorten_fname(char_u *full_path, char_u *dir_name);
-
-int expand_wildcards_eval(char_u **pat, int *num_file, char_u ***file,
-                          int flags);
-int expand_wildcards(int num_pat, char_u **pat, int *num_file, char_u *
-                     **file,
-                     int flags);
-int match_suffix(char_u *fname);
-
-int path_full_dir_name(char *directory, char *buffer, int len);
-
-int append_path(char *path, const char *to_append, int max_len);
-
-int path_is_absolute_path(const char_u *fname);
-
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "path.h.generated.h"
+#endif
 #endif