basepom-63.8

What's Changed

• add managed dep for org.apache.maven:maven-embedder by @jaredstehler in #253
• use netty-bom for managed deps, align to current in-use version by @jaredstehler in #254
• bump netty to 4.1.124 by @jaredstehler in #256
• allow system jdk < build jdk by @jaredstehler in #257
• enable toolchain for basepom builds by @jaredstehler in #259

Full Changelog: basepom-63.5...basepom-63.8