add kills to variables declared in the same scope when autodetecting

add kills to variables declared in the same scope when autodetecting

Commit 0b5e73f (add kills to variables declared in the same scope that
holds the scop, Wed Dec 16 18:35:48 2015 +0100) introduced a mechanism
for killing variables that are declared outside the scop, but it would
only do this for explicitly marked scops.  When autodetecting, there is
less need for such a mechanism because the entire function body can
often be extracted as a scop, in which case the variables declared
inside that scop are already killed.  However, this is not always
the case.  For example, the function may contain a return statement
at the end, which is currently not included in the scop.
Perform a similar killing of variables declared before the scop
and not used after the extracted scop when autodetecting.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>