ftrace: Add test to make sure compiled time sorts work

Now that ftrace function pointers are sorted at compile time, add a test
that makes sure they are sorted at run time. This test is only run if it is
configured in.

Link: https://lkml.kernel.org/r/20211206151858.4d21a24d@gandalf.local.home



Cc: Yinan Liu <yinan@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>