syscallcompat: add Faccessat
syscallcompat: add Faccessat

Add faccessat(2) with a hack for symlink, because the
kernel does not actually looks at the passed flags.

From man 2 faccessat:

   C library/kernel differences
       The  raw faccessat() system call takes only the first three argu‐
       ments.  The AT_EACCESS and AT_SYMLINK_NOFOLLOW flags are actually
       implemented  within  the  glibc wrapper function for faccessat().

rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs