Fix the PerlIO_teardown prototype to suppress a compiler warning. (Closes: #479540)

Part of upstream change 33370, also in maint-5.10.
diff --git a/perl.h b/perl.h
index e48f768..abcae45 100644
--- a/perl.h
+++ b/perl.h
@@ -3966,7 +3966,7 @@ typedef Sighandler_t Sigsave_t;
 #endif
 
 #ifdef USE_PERLIO
-EXTERN_C void PerlIO_teardown();
+EXTERN_C void PerlIO_teardown(void);
 # ifdef USE_ITHREADS
 #  define PERLIO_INIT MUTEX_INIT(&PL_perlio_mutex)
 #  define PERLIO_TERM 				\
diff --git a/perlio.c b/perlio.c
index 76fe225..b94acb0 100644
--- a/perlio.c
+++ b/perlio.c
@@ -2413,7 +2413,7 @@ PerlIO_cleanup(pTHX)
     }
 }
 
-void PerlIO_teardown() /* Call only from PERL_SYS_TERM(). */
+void PerlIO_teardown(void) /* Call only from PERL_SYS_TERM(). */
 {
     dVAR;
 #if 0
diff --git a/perliol.h b/perliol.h
index 756db2d..caba999 100644
--- a/perliol.h
+++ b/perliol.h
@@ -170,7 +170,7 @@ PERL_EXPORT_C void PerlIO_list_free(pTHX_ PerlIO_list_t *list);
 
 /* PerlIO_teardown doesn't need exporting, but the EXTERN_C is needed
  * for compiling as C++.  Must also match with what perl.h says. */
-EXTERN_C void PerlIO_teardown();
+EXTERN_C void PerlIO_teardown(void);
 
 /*--------------------------------------------------------------------------------------*/
 /* Generic, or stub layer functions */