Support Linux/AArch64 as well

Linux on AArch64 is a new platform and hence
does not provide support for the old compatibility
syscalls like e.g. SYS_fork. It offers howver
SYS_clone (which iswhat SYS_fork is being mapped to
on all other platforms anyway).
Merge pull request #83 from dirkmueller/master

AArch64 Porting (SYS_fork)