gem5 syscall emulation does not implement /proc/self/statm

[cirosantilli]

As of LKMC 6936bd6 and gem5 master 8549ee4a6dfc86a941cee0a478c01f6f2c146c3c:

./run -u userland/linux/mmap_anonymous_touch.c --emulator gem5 --gem5-worktree master --static

fails in our abort() call after our perror prints:

/proc/self/statm: No such file or directory

The abort() then makes the simulation fail slightly weirdly just as for failed asserts: #101