Documentation: LLVMLinux: Update Documentation/dontdiff

Clang has a few other kinds of derived files which shouldn't be added to a
patch. Add them to the Documentation/dontdiff file to prevent this.

Signed-off-by: Jan-Simon Möller <dl9pf@gmx.de>
Signed-off-by: Behan Webster <behanw@converseincode.com>
Cc: PaX Team <pageexec@freemail.hu>