Add 'snek_list_build' to be used with new builtin value builders

snek_list_build is a helper function for creating list values for
builtin variables.

Signed-off-by: Keith Packard <keithp@keithp.com>

snek-list.c

@@ -290,6 +290,19 @@ snek_list_imm(snek_offset_t size, snek_list_type_t type)
 	return snek_list_to_poly(list);
 }
 
+#ifdef SNEK_LIST_BUILD
+snek_poly_t
+snek_list_build(snek_list_type_t type, snek_offset_t size, ...)
+{
+	va_list args;
+	va_start(args, size);
+	snek_offset_t s = size;
+	while (s--)
+		snek_stack_push(va_arg(args, snek_poly_t));
+	return snek_list_imm(size, type);
+}
+#endif
+
 snek_list_t *
 snek_list_slice(snek_list_t *list, snek_slice_t *slice)
 {

snek.h

@@ -620,6 +620,11 @@ snek_list_mark(void *addr);
 void
 snek_list_move(void *addr);
 
+#ifdef SNEK_LIST_BUILD
+snek_poly_t
+snek_list_build(snek_list_type_t type, snek_offset_t size, ...);
+#endif
+
 /* snek-lex.c */
 
 extern uint8_t snek_lex_indent;