title: Ruby 3.0.0 seemingly doesn't use jemalloc
body: <p>I've installed <code>jemalloc</code> and followed all the guides, but it just doesn't look like <code>ruby</code> is using it:</p>
  <pre><code>$ apt install libjemalloc2
  $ ls -la /usr/lib/x86_64-linux-gnu/libjemalloc.so.2
  -rw-r--r-- 1 root root xxxxxx Feb 23  2019 /usr/lib/x86_64-linux-gnu/libjemalloc.so.2
  $ LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2 irb
  irb(main):001:0&gt; puts RbConfig::CONFIG['LIBS']
  -lm 
  irb(main):002:0&gt; puts RbConfig::CONFIG['MAINLIBS']
  -lz -lpthread -lrt -lrt -lgmp -ldl -lcrypt -lm
  </code></pre>
  <p>Does Ruby 3.0.0 require jemalloc to be loaded some other way, is the library noted somewhere else in the config or am I doing something wrong?</p>