openjdk17: regen bootstrap binaries to be smaller & more portable

- build without x11
- bundle libstdc++.so.9 & libgcc_s.so.1 from base so it works with
  base clang as well as future NetBSD releases
- don't ship external debug symbols (.diz), demos, src.zip
- build in clean chroot with pkgsrc bootstrapped to /root/pkg
- upload pgp signatures to nbftp

This mimics how it was done for openjdk11 &
takes bootstraps down from ~300MB to ~100MB.

(tnn)