make: fix GCC warnings

*** 36,51 ****
          char            *path;
          short           length;
  } pathcellt, *pathcellpt, patht;
  typedef patht           *pathpt;
  
! extern  void            add_dir_to_path(register char *path, register pathpt *pointer, register int position);
  extern  void            flush_path_cache(void);
  extern  void            flush_vroot_cache(void);
! extern  char            *get_path_name(void);
  extern  char            *get_vroot_path(register char **vroot, register char **path, register char **filename);
! extern  char            *get_vroot_name(void);
  extern  int             open_vroot(char *path, int flags, int mode, pathpt vroot_path, pathpt vroot_vroot);
  extern  pathpt          parse_path_string(register char *string, register int remove_slash);
  extern  void            scan_path_first(void);
  extern  void            scan_vroot_first(void);
  extern  void            set_path_style(int style);
--- 36,51 ----
          char            *path;
          short           length;
  } pathcellt, *pathcellpt, patht;
  typedef patht           *pathpt;
  
! extern  void            add_dir_to_path(const char *path, register pathpt *pointer, register int position);
  extern  void            flush_path_cache(void);
  extern  void            flush_vroot_cache(void);
! extern  const char      *get_path_name(void);
  extern  char            *get_vroot_path(register char **vroot, register char **path, register char **filename);
! extern  const char      *get_vroot_name(void);
  extern  int             open_vroot(char *path, int flags, int mode, pathpt vroot_path, pathpt vroot_vroot);
  extern  pathpt          parse_path_string(register char *string, register int remove_slash);
  extern  void            scan_path_first(void);
  extern  void            scan_vroot_first(void);
  extern  void            set_path_style(int style);