Linux 3.7 compat: delayed_work_timer_fn is now GPL-exported

Commit d8e794d to Linus' tree made delayed_work_timer_fn() a
GPL-exported symbol. This has forced CDDL-licensed out-of-tree modules
to adopt workarounds. ZFSOnLinux created a new interface in the Solaris
Porting Layer that provides this functionality reimplemnted this
functionality with the following commits:

zfsonlinux/spl@d9acd930b52503582425c6398fc8dbc1d7d4a01b
zfsonlinux/zfs@2ae10319624869eef0954cdfcdb6f5e33cba2e09

ZFSOnLinux and dtrace4linux share common porting issues, but they
currently implement compatibility code independently of one another.
dtrace4linux currently handles GPL-exported symbols by invoking them
anwyay. This prevents dtrace4linux from being redistributable in binary
form. My hope is that dtrace4linux will adopt the ZFSOnLinux Solaris
Porting Layer, which should resolve this issues. With that said, it is
easier to refactor a module that works than it is to refactor one that
does not. That is why I am tentatively extending the approach currently
used to handle GPL-exported symbols to cover delayed_work_timer_fn().

Signed-off-by: Richard Yao <ryao@gentoo.org>
Linux 3.8 compat: Some probe locations have been removed

sdt_add_locator is being called against some things that no longer
exist. I am adding preprocessor directives to fix that.

Signed-off-by: Richard Yao <ryao@gentoo.org>