This prevents 'tools/syscount' from using incorrect system
call descriptions if the 'ausyscall' command is not found.
In this case, it uses a lookup table as a fallback. This,
however, is compliant with x86_64 only.

For now, we fix this by raising an exception and exiting if
the 'ausyscall' executable is not available for non-x86_64
systems instead of having additional lookup tables for other
architectures.
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>