Load special libraries in-order
The `DEPS_LIBS` RPATH-substitute mechanism contains a list of paths to
load, and some of these paths are "special", in that they require more
involved loading than simply `load_library()`. These libraries are
thereby denoted by a `@` prefixing them.
Previously, we made note of these libraries, then loaded them at the end
of the loading loop, but with the addition of `libstdc++` it is now
important to have the order of the libraries (including special
libraries) to be obeyed by the loading loop, so I have inlined special
library handling into the loading loop. In the future, we may wish to
denote special libraries more explicitly than simply relying on there
being exactly three libraries, with the ordering being mapped to
`libstdc++`, `libjulia-internal`, and `libjulia-codegen`.
