Add 'struct stat' to Arch and use it for stat syscalls.
Add FREE_GUARD and use it in truncate test.
Add struct stat64 to Arch and use it for stat syscalls.
Add stack_t to Arch and use it for sigaltstack.
Add sigaltstack test.
Add 'struct sysinfo' to Arch and use it for sysinfo syscall.
Add sysinfo test.
Add 'struct utsname' to Arch and use it for uname syscall.
Improve uname test.