Use ios to support ridiculous DL_LOAD_PATH length (#59150)
Use `ios_t` as a string builder for library paths to support really long
`DL_LOAD_PATH` entries. `jl_load_dynamic_library` can't use the Julia GC
to allocate because we're called from
`JuliaOJIT::DLSymOptimizer::lookup` with `symbols_mutex` held.
Fixes #59130.
