env/windows-arm64/macstadium: add image notes and qemu script

Add barebones instructions for creating a macmini instance that runs a
Windows ARM64 buildlet in a loop. The instruction templates are from our
other macstadium builders.

See golang/go#47018 for improvements.

Updates golang/go#47018
Fixes golang/go#42604

Change-Id: I0bb092aaf99afb12a0e563a69bcb711333dda743
Reviewed-on: https://go-review.googlesource.com/c/build/+/332492
Trust: Alexander Rakoczy <alex@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

env/windows-arm64/macstadium/image-setup-notes.txt

@@ -0,0 +1,43 @@
+The Disk should be formatted with a case insensitive file system (default).
+
+System Preferences > Software Update > off
+
+System Preferences > Desktop & Screensaver > never screensaver
+
+System Preferences > Energy Saver > never sleep
+
+System Preferences > Energy Saver > start up automatically after power failure
+
+System Preferences > Sharing > enable ssh (enable for administrators)
+
+windows image:
+
+  gsutil cp gs://go-builder-data/windows-arm64.20210629.tar.xz ./windows-arm64.20210629.tar.xz
+  scp windows-arm64.20210629.tar.xz your-macmini-instance:~/
+  ssh your-macmini-instance
+  # The following will create a directory called macmini-windows with image and qemu binaries inside:
+  tar xf windows-arm64-20210629.tar.xz
+
+Automator:
+
+  scp env/windows-arm64/macstadium/winloop.sh your-macmini-instance:~/macmini-windows/winloop.sh
+  # On buildlet host:
+  chmod u+x ~/macmini-windows/winloop.sh
+  File > New > Application
+  [+] Run shell script
+  [ open -a Terminal.app $HOME/macmini-windows/winloop.sh ]
+  Save to desktop as "run-builder"
+
+System Preferences > Users & Groups > auto-login "gopher" user, run Desktop/run-builder (automator app)
+
+passwordless sudo:
+
+  sudo visudo
+  Change line from:
+   %admin ALL=(ALL) ALL
+  to:
+   %admin ALL=(ALL) NOPASSWD: ALL
+
+verbose boot: (text instead of apple image)
+
+  sudo nvram boot-args="-v"

env/windows-arm64/macstadium/winloop.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+while true; do
+  DYLD_LIBRARY_PATH="$HOME/macmini-windows/sysroot-macos-arm64/lib" "$HOME/macmini-windows/sysroot-macos-arm64/bin/qemu-system-aarch64" \
+    -L ./UTM.app/Contents/Resources/qemu \
+    -device ramfb \
+    -cpu max \
+    -smp cpus=8,sockets=1,cores=8,threads=1 \
+    -machine virt,highmem=off \
+    -accel hvf \
+    -accel tcg,tb-size=1536 \
+    -boot menu=on \
+    -m 8192 \
+    -name "Virtual Machine" \
+    -device qemu-xhci,id=usb-bus \
+    -device usb-tablet,bus=usb-bus.0 \
+    -device usb-mouse,bus=usb-bus.0 \
+    -device usb-kbd,bus=usb-bus.0 \
+    -bios "$HOME/macmini-windows/Images/QEMU_EFI.fd" \
+    -device nvme,drive=drive0,serial=drive0,bootindex=0 \
+    -drive "if=none,media=disk,id=drive0,file=$HOME/macmini-windows/Images/win10.qcow2,cache=writethrough" \
+    -device usb-storage,drive=drive2,removable=true,bootindex=1 \
+    -drive "if=none,media=cdrom,id=drive2,file=$HOME/macmini-windows/Images/virtio.iso,cache=writethrough" \
+    -device virtio-net-pci,netdev=net0 \
+    -netdev user,id=net0 \
+    -uuid 41E1CBA2-8837-4224-801B-277336D58A3D \
+    -snapshot \
+    -vnc :3
+  sleep 5
+done