PR16716 partial fix: Better types passed to _dfd_str() from syscall probes.

PR16716 partial fix: Better types passed to _dfd_str() from syscall probes.

* tapset/linux/syscalls.stp: Fixed calls to _dfd_str() in
  facessat, fchownat, futimesat, compat_futimesat, and linkat syscall
  probes.
  (syscall.futimesat): Added 'dirfd_str' variable. Fixed nesting.
  (syscall.compat_futimesat): Ditto.
* tapset/linux/nd_syscalls.stp (nd_syscall.futimesat): Added 'dirfd_str'
  variable. Fixed nesting.
  (nd_syscall.compat_futimesat): Ditto.
* tapset/linux/syscalls2.stp: Fixed calls to _dfd_str() in openat,
  readlinkat, renameat, symlinkat, unlinkat, and utimensat syscall
  probes.
  (syscall.openat): Added 'dfd' and 'dfd_str' variables.
  (syscall.readlinkat): Added 'dfd_str' variable.
  (syscall.utimensat): Added 'dfd', 'dfd_str', 'filename_uaddr',
  'filename', 'tsp_uaddr', 'flags', and 'flags_str' variables.
  (syscall.compat_utimensat): Ditto.
* tapset/linux/nd_syscalls2.stp (nd_syscall.openat): Added 'dfd' and
  'dfd_str' variables.
  (nd_syscall.readlinkat): Added 'dfd_str' variable.
  (nd_syscall.utimensat): Added 'dfd', 'dfd_str', 'filename_uaddr',
  'filename', 'tsp_uaddr', 'flags', and 'flags_str' variables.
  (nd_syscall.compat_utimensat): Ditto.
* tapset/linux/aux_syscalls.stp (_dfd_str): Improve to not ignore
  compatibility mode wrong value (instead, values passed in were fixed).
* runtime/linux/compat_unistd.h: Add '__NR_compat_futimesat' define.
* testsuite/systemtap.syscall/alarm.c: Add more tests.
* testsuite/systemtap.syscall/futimes.c: Ditto.
* testsuite/buildok/syscalls-detailed.stp: Added basic test for new
  variables.
* testsuite/buildok/syscalls2-detailed.stp: Ditto.
* testsuite/buildok/nd_syscalls-detailed.stp: Ditto.
* testsuite/buildok/nd_syscalls2-detailed.stp: Ditto.