Remove usages of weak symbols (#57523)
Inspired by a bug I hit on MinGW recently with weak symbol resolution.
I'm not sure why we started using these in
70000ac7c3d5d5f21e42555cdf99e699a246f8ec, since I believe we should be
able to lookup these symbols just fine in our `jl_exe_handle` as long as
it was linked / compiled with `-rdynamic`
Migrating away from weak symbols seems a good idea, given their uneven
implementation across platforms.
