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.  However, this approach opens the door to resolving these issues
through refactoring, so I am tentatively extending the approach
currently used to handle this to cover delayed_work_timer_fn().

My hope is that dtrace4linux will adopt the ZFSOnLinux Solaris Porting
Layer, which should resolve these issues.

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>