Simplify dispatch_o to sp_runnativecall_v if there's no result

We cannot generate dispatch_v instructions for Raku code because of sinking
semantics. But for native functions with void result we can replace dispatch_o
with sp_runnativecall_v as we know that they don't return anything.

src/spesh/disp.c

@@ -1135,12 +1135,18 @@ static int translate_dispatch_program(MVMThreadContext *tc, MVMSpeshGraph *g,
                             deopt_all_ann->data.deopt_idx);
 
                 int box_return_value = 0;
+                int has_return_value = (ins->info->opcode != MVM_OP_dispatch_v);
                 if (native) {
                     if (ins->info->opcode == MVM_OP_dispatch_o) {
                         MVMSpeshFacts *object_facts = MVM_spesh_get_facts(tc, g, temporaries[op->res_code.temp_invokee]);
                         if (object_facts->flags & MVM_SPESH_FACT_KNOWN_VALUE) {
                             MVMNativeCallBody *body = MVM_nativecall_get_nc_body(tc, object_facts->value.o);
                             switch (body->ret_type & MVM_NATIVECALL_ARG_TYPE_MASK) {
+                                case MVM_NATIVECALL_ARG_VOID:
+                                    base_op = MVM_op_get_op(MVM_OP_sp_runnativecall_v);
+                                    MVM_spesh_get_facts(tc, g, ins->operands[0])->dead_writer = 0;
+                                    has_return_value = 0;
+                                    break;
                                 case MVM_NATIVECALL_ARG_CHAR:
                                 case MVM_NATIVECALL_ARG_SHORT:
                                 case MVM_NATIVECALL_ARG_INT:
@@ -1166,7 +1172,7 @@ static int translate_dispatch_program(MVMThreadContext *tc, MVMSpeshGraph *g,
 
                 /* Write result into dispatch result register unless void. */
                 MVMuint16 cur_op = 0;
-                if (ins->info->opcode != MVM_OP_dispatch_v) {
+                if (has_return_value) {
                     if (box_return_value) {
                         rb_ins->operands[cur_op] = MVM_spesh_manipulate_get_temp_reg(tc, g, MVM_reg_int64);
                     }