build: separate build of ARM64 config
Added a pedal (VIRTIO_WIN_NO_ARM env var) that disables ARM64 build,
sometimes it's handy.
@echo off
-call tools\build.bat virtio-win.sln Win10 ARM64
+if "%VIRTIO_WIN_NO_ARM%"=="" call tools\build.bat virtio-win.sln Win10 ARM64
if errorlevel 1 goto :fail
if "%VIRTIO_WIN_NO_LEGACY%"=="" call tools\build.bat virtio-win.sln "Wxp Wnet Wlh Win7" %*
if errorlevel 1 goto :fail
