drop varargs.h support

This header file is simply out of date (for decades since at least
1989).  It's the 21st century.  Just stop using it.

compile.c

@@ -1209,7 +1209,7 @@ new_insn_body(rb_iseq_t *iseq, int line_no, enum ruby_vminsn_type insn_id, int a
     va_list argv;
     if (argc > 0) {
 	int i;
-	va_init_list(argv, argc);
+        va_start(argv, argc);
         operands = compile_data_alloc2(iseq, sizeof(VALUE), argc);
 	for (i = 0; i < argc; i++) {
 	    VALUE v = va_arg(argv, VALUE);

include/ruby/intern.h

@@ -15,11 +15,7 @@
 #include "ruby/internal/config.h"
 #include "ruby/defines.h"
 
-#ifdef HAVE_STDARG_PROTOTYPES
-# include <stdarg.h>
-#else
-# include <varargs.h>
-#endif
+#include <stdarg.h>
 
 #include "ruby/st.h"
 

vm_core.h

@@ -49,14 +49,7 @@
 
 #include <stddef.h>
 #include <signal.h>
-
-#ifdef HAVE_STDARG_PROTOTYPES
 #include <stdarg.h>
-#define va_init_list(a,b) va_start((a),(b))
-#else
-#include <varargs.h>
-#define va_init_list(a,b) va_start((a))
-#endif
 
 #include "ruby_assert.h"
 

vm_eval.c

@@ -891,7 +891,7 @@ rb_funcall(VALUE recv, ID mid, int n, ...)
     if (n > 0) {
 	long i;
 
-	va_init_list(ar, n);
+        va_start(ar, n);
 
 	argv = ALLOCA_N(VALUE, n);
 
@@ -1163,7 +1163,7 @@ rb_yield_values(int n, ...)
 	va_list args;
 	argv = ALLOCA_N(VALUE, n);
 
-	va_init_list(args, n);
+        va_start(args, n);
 	for (i=0; i<n; i++) {
 	    argv[i] = va_arg(args, VALUE);
 	}