Cannot build rust on ish due to missing /dev/shm

[andy-maier]

As a workaround to issue #2446 I tried to build rust myself, using the quickstart instructions. The './x setup' command failed when the Python script tried to create a SemLock. SO answer https://stackoverflow.com/a/34032458 suggests for a similar issue that the lack of support for /dev/shm is the reason. ish does not seem to support /dev/shm either.