torture: Make kvm-find-errors.sh notice missing vmlinux file

Currently, an obtuse compiler diagnostic can fool kvm-find-errors.sh
into believing that the build was successful.  This commit therefore
adds a check for a missing vmlinux file.  Note that in the case of
repeated torture-test scenarios ("--configs '2*TREE01'"), the vmlinux
file will only be present in the first directory, that is, in TREE01
but not TREE01.2.

Link: https://lore.kernel.org/lkml/36bd91e4-8eda-5677-7fde-40295932a640@molgen.mpg.de/Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/bin/kvm-find-errors.sh

@@ -30,10 +30,16 @@ editor=${EDITOR-vi}
 files=
 for i in ${rundir}/*/Make.out
 do
+	scenariodir="`dirname $i`"
+	scenariobasedir="`echo ${scenariodir} | sed -e 's/\.[0-9]*$//'`"
 	if egrep -q "error:|warning:|^ld: .*undefined reference to" < $i
 	then
 		egrep "error:|warning:|^ld: .*undefined reference to" < $i > $i.diags
 		files="$files $i.diags $i"
+	elif ! test -f ${scenariobasedir}/vmlinux
+	then
+		echo No ${scenariobasedir}/vmlinux file > $i.diags
+		files="$files $i.diags $i"
 	fi
 done
 if test -n "$files"