kunit: Print last test location on fault

kunit: Print last test location on fault

This helps identify the location of test faults with opportunistic calls
to _KUNIT_SAVE_LOC().  This can be useful while writing tests or
debugging them.  It is possible to call KUNIT_SUCCESS() to explicit save
last location.

Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Cc: Rae Moar <rmoar@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240408074625.65017-7-mic@digikod.net
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>