cpp: allow vastly more #defines
<inet/tcp.h> requires considerably more defines to preprocess than the
4,000 we previously allowed.  Allow an (equally arbitrary) 16,000
symbols instead.

*** 263,273 ****
  static  char            *strdex(char *, int);
  int             yywrap(void);
  int             main(int argc, char **argav);
  
  
! #define symsiz 4000
  static  struct symtab stab[symsiz];
  
  static  struct symtab *defloc;
  static  struct symtab *udfloc;
  static  struct symtab *incloc;
--- 263,273 ----
  static  char            *strdex(char *, int);
  int             yywrap(void);
  int             main(int argc, char **argav);
  
  
! #define symsiz 16000
  static  struct symtab stab[symsiz];
  
  static  struct symtab *defloc;
  static  struct symtab *udfloc;
  static  struct symtab *incloc;