build: link LLVMCoverage some more

[compnerd]

What's in this pull request?

Resolved bug number: (SR-)

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These tests seem to link against libraries needing LLVMCoverage. This fixes the
dependency.

[compnerd]

CC @rudkx

[rudkx]

Are you seeing a build failure under some configuration without these changes?

I am able to build successfully without these, and it doesn't look like SILGen/IRGen are used by either of these, which I believe is how we end up pulling in the dependency on LLVMCoverage.

[compnerd]

Yeah, I was seeing build failures under the debug configuration. (Ill try a clean build in a little while)

[rudkx]

Can you try building with 859b779 applied?

I see no linker errors on OS X with that patch, but still have four errors on Linux, which I believe are due to a difference in the way the Linux linker works.

I also committed ff25872, which resolves two of the Linux issues, but this is really just a hack that happens to work in some cases. I am looking for a more principled approach to fixing the issues there.