kcsan: test: Add a .kunitconfig to run KCSAN tests

Add a .kunitconfig file, which provides a default, working config for
running the KCSAN tests. Note that it needs to run on an SMP machine, so
to run under kunit_tool, the --qemu_args option should be used (on a
supported architecture, like x86_64). For example:
./tools/testing/kunit/kunit.py run --arch=x86_64 --qemu_args='-smp 8'
					--kunitconfig=kernel/kcsan
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Acked-by: Brendan Higgins <brendanhiggins@google.com>
Tested-by: Daniel Latypov <dlatypov@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

kernel/kcsan/.kunitconfig

+# Note that the KCSAN tests need to run on an SMP setup.
+# Under kunit_tool, this can be done by using the --qemu_args
+# option to configure a machine with several cores. For example:
+# ./tools/testing/kunit/kunit.py run --kunitconfig=kernel/kcsan \
+# 				 --arch=x86_64 --qemu_args="-smp 8"
+
+CONFIG_KUNIT=y
+
+CONFIG_DEBUG_KERNEL=y
+
+# Need some level of concurrency to test a concurrency sanitizer.
+CONFIG_SMP=y
+
+CONFIG_KCSAN=y
+CONFIG_KCSAN_KUNIT_TEST=y
+
+# Set these if you want to run test_barrier_nothreads
+#CONFIG_KCSAN_STRICT=y
+#CONFIG_KCSAN_WEAK_MEMORY=y
+
+# This prevents the test from timing out on many setups. Feel free to remove
+# (or alter) this, in conjunction with setting a different test timeout with,
+# for example, the --timeout kunit_tool option.
+CONFIG_KCSAN_REPORT_ONCE_IN_MS=100