QEMU insists on using /var/tmp instead of /tmp
Description of problem:
On a host, our sysadmins have decided for whatever reason that `/var/tmp` is not a thing that normal users can write to (and perhaps that's dumb, but it is what it is and would be a challenging non-technical problem to solve). Whenever QEMU detects the temporary directory is /tmp, it changes it to `/var/tmp` without a mechanism to change it (see https://gitlab.com/qemu-project/qemu/-/commit/69fbfff95e849156985cf95e2010ffc8762e34e6).

I'm sure in the general case this is fine, but can you add an environment variable or a ./configure option to make this location configurable? I really would like to write to `/tmp`.