well-defined listing order for machine types

Commit 261747f1 ("vl: Use MachineClass instead of global QEMUMachine
list") broke the ordering of the machine types in the user-visible output
of

  qemu-system-XXXX -M \?

This occurred because registration was rebased from a manually maintained
linked list to GLib hash tables:

  qemu_register_machine()
    type_register()
      type_register_internal()
        type_table_add()
          g_hash_table_insert()

and because the listing was rebased accordingly, from the traversal of the
list to the traversal of the hash table (rendered as an ad-hoc list):

  machine_parse()
    object_class_get_list(TYPE_MACHINE)
      object_class_foreach()
        g_hash_table_foreach()

The current order is a "random" one, for practical purposes, which is
annoying for users.

Introduce new members QEMUMachine.family and MachineClass.family, allowing
machine types to be "clustered". Introduce a comparator function that
establishes a total ordering between machine types, ordering machine types
in the same family next to each other. In machine_parse(), list the
supported machine types sorted with the comparator function.

The comparator function:
- sorts whole families before standalone machine types,
- sorts whole families between each other in alphabetically increasing
  order,
- sorts machine types inside the same family in alphabetically decreasing
  order,
- sorts standalone machine types between each other in alphabetically
  increasing order.

After this patch, all machine types are considered standalone, and
accordingly, the output is alphabetically ascending. This will be refined
in the following patches.

Effects on the x86_64 output:

Before:

> Supported machines are:
> pc-0.13              Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-2.0        Standard PC (i440FX + PIIX, 1996)
> pc-1.0               Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-2.1        Standard PC (i440FX + PIIX, 1996)
> pc-q35-1.7           Standard PC (Q35 + ICH9, 2009)
> pc-1.1               Standard PC (i440FX + PIIX, 1996)
> pc-0.14              Standard PC (i440FX + PIIX, 1996)
> pc-q35-2.0           Standard PC (Q35 + ICH9, 2009)
> pc-i440fx-1.4        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-1.5        Standard PC (i440FX + PIIX, 1996)
> pc-0.15              Standard PC (i440FX + PIIX, 1996)
> pc-q35-1.4           Standard PC (Q35 + ICH9, 2009)
> isapc                ISA-only PC
> pc                   Standard PC (i440FX + PIIX, 1996) (alias of pc-i440fx-2.2)
> pc-i440fx-2.2        Standard PC (i440FX + PIIX, 1996) (default)
> pc-1.2               Standard PC (i440FX + PIIX, 1996)
> pc-0.10              Standard PC (i440FX + PIIX, 1996)
> pc-0.11              Standard PC (i440FX + PIIX, 1996)
> pc-q35-2.1           Standard PC (Q35 + ICH9, 2009)
> q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-2.2)
> pc-q35-2.2           Standard PC (Q35 + ICH9, 2009)
> pc-i440fx-1.6        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-1.7        Standard PC (i440FX + PIIX, 1996)
> none                 empty machine
> pc-q35-1.5           Standard PC (Q35 + ICH9, 2009)
> pc-q35-1.6           Standard PC (Q35 + ICH9, 2009)
> pc-0.12              Standard PC (i440FX + PIIX, 1996)
> pc-1.3               Standard PC (i440FX + PIIX, 1996)

After:

> Supported machines are:
> isapc                ISA-only PC
> none                 empty machine
> pc-0.10              Standard PC (i440FX + PIIX, 1996)
> pc-0.11              Standard PC (i440FX + PIIX, 1996)
> pc-0.12              Standard PC (i440FX + PIIX, 1996)
> pc-0.13              Standard PC (i440FX + PIIX, 1996)
> pc-0.14              Standard PC (i440FX + PIIX, 1996)
> pc-0.15              Standard PC (i440FX + PIIX, 1996)
> pc-1.0               Standard PC (i440FX + PIIX, 1996)
> pc-1.1               Standard PC (i440FX + PIIX, 1996)
> pc-1.2               Standard PC (i440FX + PIIX, 1996)
> pc-1.3               Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-1.4        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-1.5        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-1.6        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-1.7        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-2.0        Standard PC (i440FX + PIIX, 1996)
> pc-i440fx-2.1        Standard PC (i440FX + PIIX, 1996)
> pc                   Standard PC (i440FX + PIIX, 1996) (alias of pc-i440fx-2.2)
> pc-i440fx-2.2        Standard PC (i440FX + PIIX, 1996) (default)
> pc-q35-1.4           Standard PC (Q35 + ICH9, 2009)
> pc-q35-1.5           Standard PC (Q35 + ICH9, 2009)
> pc-q35-1.6           Standard PC (Q35 + ICH9, 2009)
> pc-q35-1.7           Standard PC (Q35 + ICH9, 2009)
> pc-q35-2.0           Standard PC (Q35 + ICH9, 2009)
> pc-q35-2.1           Standard PC (Q35 + ICH9, 2009)
> q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-2.2)
> pc-q35-2.2           Standard PC (Q35 + ICH9, 2009)

Effects on the aarch64 output:

Before:

> Supported machines are:
> lm3s811evb           Stellaris LM3S811EVB
> canon-a1100          Canon PowerShot A1100 IS
> vexpress-a15         ARM Versatile Express for Cortex-A15
> vexpress-a9          ARM Versatile Express for Cortex-A9
> xilinx-zynq-a9       Xilinx Zynq Platform Baseboard for Cortex-A9
> connex               Gumstix Connex (PXA255)
> n800                 Nokia N800 tablet aka. RX-34 (OMAP2420)
> lm3s6965evb          Stellaris LM3S6965EVB
> versatileab          ARM Versatile/AB (ARM926EJ-S)
> borzoi               Borzoi PDA (PXA270)
> tosa                 Tosa PDA (PXA255)
> cheetah              Palm Tungsten|E aka. Cheetah PDA (OMAP310)
> midway               Calxeda Midway (ECX-2000)
> mainstone            Mainstone II (PXA27x)
> n810                 Nokia N810 tablet aka. RX-44 (OMAP2420)
> terrier              Terrier PDA (PXA270)
> highbank             Calxeda Highbank (ECX-1000)
> cubieboard           cubietech cubieboard
> sx1-v1               Siemens SX1 (OMAP310) V1
> sx1                  Siemens SX1 (OMAP310) V2
> realview-eb-mpcore   ARM RealView Emulation Baseboard (ARM11MPCore)
> kzm                  ARM KZM Emulation Baseboard (ARM1136)
> akita                Akita PDA (PXA270)
> z2                   Zipit Z2 (PXA27x)
> musicpal             Marvell 88w8618 / MusicPal (ARM926EJ-S)
> realview-pb-a8       ARM RealView Platform Baseboard for Cortex-A8
> versatilepb          ARM Versatile/PB (ARM926EJ-S)
> realview-eb          ARM RealView Emulation Baseboard (ARM926EJ-S)
> realview-pbx-a9      ARM RealView Platform Baseboard Explore for Cortex-A9
> spitz                Spitz PDA (PXA270)
> none                 empty machine
> virt                 ARM Virtual Machine
> collie               Collie PDA (SA-1110)
> smdkc210             Samsung SMDKC210 board (Exynos4210)
> verdex               Gumstix Verdex (PXA270)
> nuri                 Samsung NURI board (Exynos4210)
> integratorcp         ARM Integrator/CP (ARM926EJ-S)

After:

> Supported machines are:
> akita                Akita PDA (PXA270)
> borzoi               Borzoi PDA (PXA270)
> canon-a1100          Canon PowerShot A1100 IS
> cheetah              Palm Tungsten|E aka. Cheetah PDA (OMAP310)
> collie               Collie PDA (SA-1110)
> connex               Gumstix Connex (PXA255)
> cubieboard           cubietech cubieboard
> highbank             Calxeda Highbank (ECX-1000)
> integratorcp         ARM Integrator/CP (ARM926EJ-S)
> kzm                  ARM KZM Emulation Baseboard (ARM1136)
> lm3s6965evb          Stellaris LM3S6965EVB
> lm3s811evb           Stellaris LM3S811EVB
> mainstone            Mainstone II (PXA27x)
> midway               Calxeda Midway (ECX-2000)
> musicpal             Marvell 88w8618 / MusicPal (ARM926EJ-S)
> n800                 Nokia N800 tablet aka. RX-34 (OMAP2420)
> n810                 Nokia N810 tablet aka. RX-44 (OMAP2420)
> none                 empty machine
> nuri                 Samsung NURI board (Exynos4210)
> realview-eb          ARM RealView Emulation Baseboard (ARM926EJ-S)
> realview-eb-mpcore   ARM RealView Emulation Baseboard (ARM11MPCore)
> realview-pb-a8       ARM RealView Platform Baseboard for Cortex-A8
> realview-pbx-a9      ARM RealView Platform Baseboard Explore for Cortex-A9
> smdkc210             Samsung SMDKC210 board (Exynos4210)
> spitz                Spitz PDA (PXA270)
> sx1                  Siemens SX1 (OMAP310) V2
> sx1-v1               Siemens SX1 (OMAP310) V1
> terrier              Terrier PDA (PXA270)
> tosa                 Tosa PDA (PXA255)
> verdex               Gumstix Verdex (PXA270)
> versatileab          ARM Versatile/AB (ARM926EJ-S)
> versatilepb          ARM Versatile/PB (ARM926EJ-S)
> vexpress-a15         ARM Versatile Express for Cortex-A15
> vexpress-a9          ARM Versatile Express for Cortex-A9
> virt                 ARM Virtual Machine
> xilinx-zynq-a9       Xilinx Zynq Platform Baseboard for Cortex-A9
> z2                   Zipit Z2 (PXA27x)

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1145042
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel.a@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>


