List softmmu fuzz targets in 'make help' output:

  $ make help
  ...
  Architecture specific targets:
  aarch64-softmmu/all            - Build for aarch64-softmmu
  aarch64-softmmu/fuzz           - Build fuzzer for aarch64-softmmu
  alpha-softmmu/all              - Build for alpha-softmmu
  alpha-softmmu/fuzz             - Build fuzzer for alpha-softmmu
  arm-softmmu/all                - Build for arm-softmmu
  arm-softmmu/fuzz               - Build fuzzer for arm-softmmu
  ...

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200514143433.18569-3-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>