#1945 Make hpc-related activity conditional on --enable-library-coverage flag

Instead of applying hpc flags directly via 'enableCoverage' I've added a 'withCoverage' flag to LocalBuildInfo that is then checked before setting HPXTIXFILE or calling 'markupTest' or 'markupPackage' and used to generate -fhpc and -hpcdir flags in the GHC-specific code.

Added initially-failing now passing tests to PackageTests/TestSuiteExeV10.
I believe there is a difference between `Nothing` and `Just []` as the former results in inheriting the environment while the latter results in an empty environment, hence the use of `getEffectiveEnvironment`.

It makes sense to me to also reflect the distinction in the output as `rawSystemIOWithEnv` currently does. As such I have currently duplicated the maybe call.