find_package(lttng-ust REQUIRED) fails to find the lttng library without
this change. because find_path(LTTNG_LIBRARY_DIR ...) does not search
in the default library paths. and the second mode of
FIND_PACKAGE_HANDLE_STANDARD_ARGS() does not stop the cmake with a fatal
message, even some of the required vars are missing. so use the
implemetantion from cmake upstream.
Signed-off-by: Kefu Chai <kchai@redhat.com>
Kefu Chai