contrib: add `--relative-rpath` option to `juliac.jl` (#57199)
This flag is useful when you'd like to deploy the generated library /
executable across machines. This will tell the linker to look for the
required libraries (`libjulia*.so`, `libopenblas`, etc.) in an adjacent
`julia/` directory.
We'll eventually use PackageCompiler to help bundle all the required
libraries together, but for now this at least gets the lookup setup
correctly in the created `.so` / binary.
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Co-authored-by: Gabriel Baraldi <baraldigabriel@gmail.com>
