A symlink to i386 includes is created in the build dir on amd64 since
freebsd/freebsd-src@d07600c563
Tell git to ignore it like the other include links.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes#13719