ppc64 - unresolved traget-symbols $fd

[Hien Nguyen]

This issue might be duplicated in #2438

stap -up4 -vv -e'probe syscall.fstat{}'
....
semantic error: unresolved target-symbol expression: identifier '$fd' at 
/root/stap_testing_200606121452/src/tapset/syscalls.stp:697:12
semantic error: unresolved target-symbol expression: identifier '$fd' at 
/root/stap_testing_200606121452/src/tapset/syscalls.stp:699:31
....