rcutorture: Add --buildonly dry-run capability

This commit adds --buildonly, which does the builds specified by the
--configs argument, but does not boot or test the resulting kernels.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
diff --git a/tools/testing/selftests/rcutorture/bin/kvm-test-1-rcu.sh b/tools/testing/selftests/rcutorture/bin/kvm-test-1-rcu.sh
index 93342f7..3df1581 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-test-1-rcu.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-test-1-rcu.sh
@@ -141,6 +141,11 @@
 boot_args="$boot_args rcutorture.stat_interval=15 rcutorture.shutdown_secs=$seconds rcutorture.rcutorture_runnable=1"
 
 echo $QEMU $qemu_args -m 512 -kernel $builddir/arch/x86/boot/bzImage -append \"$qemu_append $boot_args\" > $resdir/qemu-cmd
+if test -n "$RCU_BUILDONLY"
+then
+	echo Build-only run specified, boot/test omitted.
+	exit 0
+fi
 $QEMU $qemu_args -m 512 -kernel $builddir/arch/x86/boot/bzImage -append "$qemu_append $boot_args" &
 qemu_pid=$!
 commandcompleted=0