Fix Python 3 checksum regression from 8341c4e

The Linux kernel won't autocreate /dev/shm inside devtmpfs.
Without it, semaphores won't work properly in Python.

Previously, /dev/shm was set up in populate_device_nodes, but we
no longer run that after booting into Linux.

Author: Googulator

steps/improve/finalize_fhs.sh

@@ -21,6 +21,7 @@ mount | grep '/proc' &> /dev/null || (mkdir -p /proc; mount -t proc proc /proc)
 mount | grep '/sys' &> /dev/null || (mkdir -p /sys; mount -t sysfs sysfs /sys)
 # Make /tmp a ramdisk (speeds up configure etc significantly)
 mount | grep '/tmp' &> /dev/null || (mkdir -p /tmp; mount -t tmpfs tmpfs /tmp)
+mount | grep '/dev/shm' &> /dev/null || (mkdir -p /dev/shm; mount -t tmpfs tmpfs /dev/shm)
 
 # Add /etc/resolv.conf
 echo 'nameserver 1.1.1.1' > /etc/resolv.conf