Allow switching between linkers

There are multiple drop-in replacement Unix linkers like, for example, [mold](https://github.com/rui314/mold). This could potentially speed up the PackageCompiler build time. Can an option or documentation be added to allow setting a different linker?

Start by tracing how PackageCompiler invokes the Unix linker during a package build; the issue does not name a file, test, or entry point. Determine whether a configurable linker option or documentation is appropriate, then verify that an alternative such as mold can be selected and that the documented behavior works.

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