Compile jemalloc with Ruby interpreter

Currently we dynamically load jemalloc via the LD_PRELOAD environment variable, but this causes seg faults on systems with certain applications running (e.g. anti-virus software like Cylance: #3813 (closed), #4330 (closed)).

I suspect we'll have better success if the Ruby interpreter is actually compiled using the --with-jemalloc command-line. Note that Redis already does this by default.

Note there is an issue in the Ruby interpreter tracker about making this the default: https://bugs.ruby-lang.org/issues/14718