Make /tmp really temporary

[mingfang]

Building images sometimes leaves scratch files in the /tmp directory.
In addition sometimes I need to ADD my project's source code during a build, but I don't want the source to remain after the build.
By making /tmp temporary, then I can do simply ADD src /tmp/src.

[phemmer]

I think #10310 accomplishes what you're after.

[mingfang]

That sounds more sophisticated then what I need.
I just wanted /tmp to behave "normal"; /tmp on Linux do not survive a reboot.
The ability to ADD src there for building is just an additional benefit.

[phemmer]

On my distro, /tmp does survive a reboot. This would not be "normal" from my perspective.
Also, if /tmp is made to not survive outside the container, this wouldn't work for builds. During builds, each command in the Dockerfile is its own container. Thus the data would be gone on the next command.

[mingfang]

Based on the comments here I'm closing this issue.
I also created a new issue to specifically address the ability to avoid source code to end up in a layer, #12169