c variadic calls

compiler/ir/ir.odin

@@ -87,6 +87,7 @@ Opcode :: enum u8 {
 	Orelse_Begin,
 	Orelse,
 	Widen,
+	C_Vararg_Promote,
 	Weaken_Pointer,
 	Neg_Checked,
 	Add_Checked,
@@ -115,6 +116,7 @@ Function :: struct {
 	implementation:     Implementation,
 	linkage:            Linkage,
 	is_main:            bool,
+	variadic:           bool,
 	param_types:        []types.Type,
 	result:             types.Type,
 	instructions:       []Instruction,