Make these buildable on arm64-linux.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13821 a5019735-40e9-0310-863c-91ae7b9d1cf9
First attempt at supporting sys_clone.
Also enable: sys_exit, sys_nanosleep, sys_madvise.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13822 a5019735-40e9-0310-863c-91ae7b9d1cf9