jemalloc: Update to handle additional build flags

[sallustfire]

The build is updated to handle setting a private namespace and conf during the build. Minor refactoring and fixes to prof tests.

[bazel-io]

Hello @bazelbuild/bcr-maintainers, modules without existing maintainers (jemalloc) have been updated in this PR.
Please review the changes. You can view a diff against the previous version in the "Generate module diff" check.

[sallustfire]

@bazelbuild/bcr-maintainers Is there a way that I can get added to the list of maintainers for this module? This c module is more than just a single BUILD file. I've been asked a couple times now to help others with functionality and maintenance but a commit was also pushed through quickly without any discussion or syncing of the repo that generates the overlay.