Rollup merge of #56986 - alexcrichton:move-jemalloc, r=Mark-Simulacrum

rustc: Move jemalloc from rustc_driver to rustc

This commit moves jemalloc to just the rustc binary rather than the
rustc_driver shared library, enusring that it's only used for binaries
that opt-in to it like rustc rather than other binaries using
librustc_driver like rustdoc/rls/etc. This will hopefully address #56980

diff --cc Cargo.lock
Simple merge

diff --cc src/librustc_driver/lib.rs
Simple merge