Lookup libraries in `libjulia-*` before `jl_exe_handle`
We do not use `dlvsym` to separate the symbols between multiple copies
of libjulia, instead preferring to resolve symbols directly against the
appropriate internal library handle.
During bootstrapping, many internal symbols (e.g. `jl_fl_parse`) are
available in the global EXE namespace, so we need to adapt our search
order to resolve symbols in internal libraries first.
With this fix, no sysimage symbols are resolved to `jl_exe_handle`
(which is generally broken in Julia-in-Julia scenarios):
```
$ cat objdump_after.txt | grep libjulia_internal_handle | wc
1131 14703 145899
$ cat objdump_after.txt | grep jl_exe_handle | wc
0 0 0
```
versus before:
```
$ cat objdump_before.txt | grep libjulia_internal_handle | wc
577 7501 74433
$ cat objdump_before.txt | grep jl_exe_handle | wc
554 7202 63710
```
