leaving a module out of test-suite/other-modules yields a cryptic linker error

[erikkaplun]

Consider https://github.com/eallik/mergesort

If the TestProperties module is accidentally left out of test/suite/other-modules in the .cabal file, cabal test yields a cryptic error message shown in erroroutput.txt; this is at commit c4dbd6c; commit 6887d16 fixes the problem and cabal test works just fine from then on.

My "complaint" here is that cabal should print a human friendly error message about the situation, instead of letting the linker fail; i.e. it should notice there's a problem, instead of handing over to the linker only for it to fail in a way that is almost completely undiagnosable for a beginner like myself.

[ttuegel]

This is a duplicate of #1746.