Include tests directories in the linker legacy configuration.

Make ld.config.legacy.txt similar to other linker configurations with
respect to tests in /data/{nativetest,benchmarktest}{,64}.

Note: The linker legacy configuration is used by the ART generic build
targets, defined in project device/generic/art.

Test: ART chroot-based on-device testing using the master-art
Bug: 121117762
Change-Id: I6c8fafa2568862e450aa7b9fea1177a184cb9705