torture: Make kvm-recheck.sh skip kcsan.sum for build-only runs

Currently, kvm-recheck.sh attempts to create a kcsan.sum file even for
build-only runs.  This results in false-positive bash errors due to
there being no console.log files in that case.  This commit therefore
makes kvm-recheck.sh skip creating the kcsan.sum file for build-only runs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/bin/kvm-recheck.sh

@@ -74,7 +74,10 @@ do
 	done
 	if test -f "$rd/kcsan.sum"
 	then
-		if grep -q CONFIG_KCSAN=y $T
+		if ! test -f $T
+		then
+			:
+		elif grep -q CONFIG_KCSAN=y $T
 		then
 			echo "Compiler or architecture does not support KCSAN!"
 			echo Did you forget to switch your compiler with '--kmake-arg CC=<cc-that-supports-kcsan>'?