Merge r197808 from head to stable/8:

Merge r197808 from head to stable/8:

  In rtld's map_object(), use pread(..., 0) rather than read() to read the
  ELF header from the front of the file.  As all other I/O on the binary
  is done using mmap(), this avoids the need for seek privileges on the
  file descriptor during run-time linking.

  Sponsored by: Google

git-svn-id: svn://svn.freebsd.org/base/stable/8@200509 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f