错误：

==> Downloading https://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.2/FD12FLOPPY.zip
curl: (22) The requested URL returned error: 404

Error: qemu-virgl: Failed to download resource "qemu-virgl--test-image"
Download failed: https://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.2/FD12FLOPPY.zip

解决方法：

执行以下命令会打开一个文件，修改里面的url

brew edit qemu-virgl

 将其改成：http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.2/official/FD12FLOPPY.zip 

然后重新执行就OK了

brew install qemu-virgl