testsuite driver is sensitive to registration of multiple boot package versions

Currently testsuite/tests/Makefile generates the --rootdir flags to be passed by runtests.py by looking at the output of ghc-pkg list. In the case that the user has recently bumped their submodules this list may contain multiple versions of the same package. This will then result in the same library/$LIB/tests directory being passed to the testsuite driver more than once. The testsuite driver will then squawk a "There are multiple tests with this name" warning. It took a few minutes for Simon and I to work out why this was.

We should do better here (at least in Hadrian). Either by:

• Teaching the testsuite driver to deduplicate the --rootdir list
• Using a more robust source for the list of tested packages

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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changed weight to 5

added Tbug Trac import labels

CCing Alp as we recently the discussed the state of the testsuite in Hadrian.

Do we have such a "more robust source" ? I think we can easily deduplicate, but if we do have such a source of rootdirs/packages to test, that would quite likely be simpler and a better choice in the long run.

added Pnormal label