make: fix GCC warnings

*** 67,80 ****
  
  /*
   * Static variables
   */
  #ifdef SUN5_0
! extern "C" void         (*sigivalue)(int) = SIG_DFL;
! extern "C" void         (*sigqvalue)(int) = SIG_DFL;
! extern "C" void         (*sigtvalue)(int) = SIG_DFL;
! extern "C" void         (*sighvalue)(int) = SIG_DFL;
  #else
  static  void            (*sigivalue)(int) = (void (*) (int)) SIG_DFL;
  static  void            (*sigqvalue)(int) = (void (*) (int)) SIG_DFL;
  static  void            (*sigtvalue)(int) = (void (*) (int)) SIG_DFL;
  static  void            (*sighvalue)(int) = (void (*) (int)) SIG_DFL;
--- 67,82 ----
  
  /*
   * Static variables
   */
  #ifdef SUN5_0
! extern "C" {
!         void            (*sigivalue)(int) = SIG_DFL;
!         void            (*sigqvalue)(int) = SIG_DFL;
!         void            (*sigtvalue)(int) = SIG_DFL;
!         void            (*sighvalue)(int) = SIG_DFL;
! }
  #else
  static  void            (*sigivalue)(int) = (void (*) (int)) SIG_DFL;
  static  void            (*sigqvalue)(int) = (void (*) (int)) SIG_DFL;
  static  void            (*sigtvalue)(int) = (void (*) (int)) SIG_DFL;
  static  void            (*sighvalue)(int) = (void (*) (int)) SIG_DFL;
*** 323,333 ****
   *              char_semantics  The vector of character semantics that we set
   */
  void
  setup_char_semantics(void)
  {
!         char            *s;
          wchar_t         wc_buffer[1];
          int             entry;
  
          if (svr4) {
                  s = "@-";
--- 325,335 ----
   *              char_semantics  The vector of character semantics that we set
   */
  void
  setup_char_semantics(void)
  {
!         const char      *s;
          wchar_t         wc_buffer[1];
          int             entry;
  
          if (svr4) {
                  s = "@-";
*** 411,421 ****
   *              format          printf type format string
   *              args            Arguments to match the format
   */
  /*VARARGS*/
  void
! fatal_mksh(char * message, ...)
  {
          va_list args;
          char    *buf = static_buf;
          char    *mksh_fat_err = catgets(libmksdmsi18n_catd, 1, 128, "mksh: Fatal error: ");
          char    *cur_wrk_dir = catgets(libmksdmsi18n_catd, 1, 129, "Current working directory: ");
--- 413,423 ----
   *              format          printf type format string
   *              args            Arguments to match the format
   */
  /*VARARGS*/
  void
! fatal_mksh(const char *message, ...)
  {
          va_list args;
          char    *buf = static_buf;
          char    *mksh_fat_err = catgets(libmksdmsi18n_catd, 1, 128, "mksh: Fatal error: ");
          char    *cur_wrk_dir = catgets(libmksdmsi18n_catd, 1, 129, "Current working directory: ");
*** 466,476 ****
   *              format          printf style format string
   *              args            arguments to match the format
   */
  /*VARARGS*/
  void
! fatal_reader_mksh(char * pattern, ...)
  {
          va_list args;
          char    message[1000];
  
          va_start(args, pattern);
--- 468,478 ----
   *              format          printf style format string
   *              args            arguments to match the format
   */
  /*VARARGS*/
  void
! fatal_reader_mksh(const char * pattern, ...)
  {
          va_list args;
          char    message[1000];
  
          va_start(args, pattern);