machine: query mem-merge machine property

Running
    qemu-bin ... -machine pc,mem-merge=on
leads to crash:
    x86_64-softmmu/qemu-system-x86_64 -machine pc,dump-guest-core=on
    qemu-system-x86_64: qemu/util/qemu-option.c:387: qemu_opt_get_bool_helper:
    Assertion `opt->desc && opt->desc->type == QEMU_OPT_BOOL' failed.  Aborted
    (core dumped)

This happens because the commit e79d5a6 ("machine: remove qemu_machine_opts
global list") removed the global option descriptions and moved them to
MachineState's QOM properties.

Fix this by querying machine properties through designated wrappers.
Signed-off-by: NMarcel Apfelbaum <marcel@redhat.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>

exec.c

@@ -1326,7 +1326,7 @@ void qemu_ram_unset_idstr(ram_addr_t addr)
 
 static int memory_try_enable_merging(void *addr, size_t len)
 {
-    if (!qemu_opt_get_bool(qemu_get_machine_opts(), "mem-merge", true)) {
+    if (!machine_mem_merge(current_machine)) {
         /* disabled by the user */
         return 0;
     }

hw/core/machine.c

@@ -286,6 +286,7 @@ static void machine_initfn(Object *obj)
     ms->kernel_irqchip_allowed = true;
     ms->kvm_shadow_mem = -1;
     ms->dump_guest_core = true;
+    ms->mem_merge = true;
 
     object_property_add_str(obj, "accel",
                             machine_get_accel, machine_set_accel, NULL);
@@ -431,6 +432,11 @@ bool machine_dump_guest_core(MachineState *machine)
     return machine->dump_guest_core;
 }
 
+bool machine_mem_merge(MachineState *machine)
+{
+    return machine->mem_merge;
+}
+
 static const TypeInfo machine_info = {
     .name = TYPE_MACHINE,
     .parent = TYPE_OBJECT,

include/hw/boards.h

@@ -74,6 +74,7 @@ bool machine_kernel_irqchip_required(MachineState *machine);
 int machine_kvm_shadow_mem(MachineState *machine);
 int machine_phandle_start(MachineState *machine);
 bool machine_dump_guest_core(MachineState *machine);
+bool machine_mem_merge(MachineState *machine);
 
 /**
  * MachineClass: