Add __x64_ for Linux 4.17

[andrewkroh]

Linux 4.17 change krobe naming. It adds a __x64_ to 64-bit syscalls names.

$ cat /proc/kallsyms | grep execve | grep x64_
0000000000000000 T __x64_sys_execve
0000000000000000 T __x64_sys_execveat