Feat/syscall busybox

Hyf/busybox

Don't assert "flags == 0" in sys_unlinkat

create /proc and /proc/mounts before starting busybox

sys_fstatat should return what vfs_ext_stat returns

It's because we use an atomic variable for ext4_lock/unlock. When we use semaphore, everything works well.

Not tested on ext4.

next step is to refactor syscalls