Adjust sanitizers for FreeBSD 64-bit inode update

Summary:
Very recently, FreeBSD 12 has been updated to use 64-bit inode numbers:
<https://svnweb.freebsd.org/changeset/base/318737>.  This entails many
user-visible changes, but for the sanitizers the modifications are
limited in scope:
* The `stat` and `lstat` syscalls were removed, and should be replaced
  with calls to `fstatat`.
* The `getdents` syscall was removed, and should be replaced with calls
  to `getdirentries`.
* The layout of `struct dirent` was changed to accomodate 64-bit inode
  numbers, and a new `d_off` field was added.
* The system header <sys/_types.h> now contains a macro `__INO64` to
  determine whether the system uses 64-bit inode numbers.

I tested these changes on both FreeBSD 12.0-CURRENT (after r318959,
which adds the `__INO64` macro), and FreeBSD 11.0-STABLE (which still
uses 32-bit inode numbers).

Reviewers: emaste, kcc, vitalybuka, kubamracek

Reviewed By: vitalybuka

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33600

llvm-svn: 304658