#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.
Very well. Any better suggestion then than simply duplicating the following lines from `rawSystemIOWithEnv` in `PackageTests.PackageTester.run`, which my change was intended to avoid?

    maybe (printRawCommandAndArgs       verbosity path args)
          (printRawCommandAndArgsAndEnv verbosity path args) menv

I had overlooked the distinction you point out, which is interesting, though I honestly have no idea whether it is significant.Thanks for taking the time to review this by the way, it will be satisfying to see it merged.