* Before this it was compiled but not used, because TruffleRuby has
a stringio.rb in stdlib and .rb has precedence over .so.
In fact that extension never worked on TruffleRuby,
because rb_io_extract_modeenc() has never been defined on TruffleRuby.
* So this just skip compiling the extension since compilation of it now fails:
https://github.com/ruby/openssl/issues/699d791b63df6