をビルドしてみたら

…
/usr/local/src/ruby-2.6.0/.ext/common/openssl/buffering.rb:1: unknown encoding name: binary (ArgumentError)
    …
uncommon.mk:364: recipe for target 'do-install-all' failed
make: *** [do-install-all] Error 1
Command exited with non-zero status 2

だそーな。