JDK-8252395, it was possible to build without external debuginfo by setting STRIP_POLICY=no_strip. This has been the case throughout the life of 8u. See also JDK-8207234.
JDK-8252395 assumes that ENABLE_DEBUG_SYMBOLS being true is a sufficient check. JDK-8252975 added a check on POST_STRIP_CMD, but this is still not sufficient to give the old behaviour.