Fixed build errors integrating upstream qemu configure fixes

[valerino]

tested on ubuntu 18.04

[steev]

I don't think turning off Werror is the way to go.

The usb error is fixed via qemu/qemu@121829c this commit.

host-libusb is fixed with qemu/qemu@9d8fa0d which deals with the libusb deprecation but allows people to build still with older versions of libusb.

And, the VTE issue can be done with this commit.
qemu/qemu@82a4f1a#diff-e0320540bef9fc439412c472e5324303

The VTE changes actually change more upstream but since luaqemu still seems to be based on qemu 2.9.50 while upstream is 2.12, these 3 patches are all that are needed. Ideally, moving to 2.12 is best, and keeping up with upstream. I've looked into it briefly but a lot of hunks for the luajit patch fail and I haven't got the time to go through them just yet (not a developer of luaqemu, just interested in using it)