Hardwired path in doctest's own testsuite breaks with v2-cabal

[andreasabel]

This non-portable path makes cabal v2-test fail for doctest itself:

doctest/test/MainSpec.hs

Line 110 in f862507

doctest "with-cbits" ["Bar.hs", "../../../dist/build/spec/spec-tmp/test/integration/with-cbits/foo.o"]

With v2-cabal and ghc-9.0.1 the path becomes ../../../dist-newstyle/build/x86_64-osx/ghc-9.0.1/doctest-0.19/t/spec/build/spec/spec-tmp/Test/integration/with-cbits/foo.o.

Maybe related: #245

[andreasabel]

This is still deactivated:

doctest/test/MainSpec.hs

Lines 109 to 120 in 6bb14c4

	-- Andreas, 2021-02-27, see issue #294.
	-- This test case contains a hard-wired path that does not work
	-- with v2-cabal.
	-- I tested it under v2-cabal with a very non-portable path.
	-- Deactivating the test case until a systematic solution is found...
	--
	-- it "works with additional object files" $ do
	-- -- -- Path for v1-cabal:
	-- -- doctest "with-cbits" ["Bar.hs", "../../../dist/build/spec/spec-tmp/test/integration/with-cbits/foo.o"]
	-- -- -- Path for v2-cabal with ghc-9.0.1
	-- -- doctest "with-cbits" ["Bar.hs", "../../../dist-newstyle/build/x86_64-osx/ghc-9.0.1/doctest-0.19/t/spec/build/spec/spec-tmp/Test/integration/with-cbits/foo.o"]
	-- (cases 1)