#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'm in favour of leaving these two functions separate: it's not immediately obvious what `Nothing` stands for in `printRawCommandAndArgs verbosity path args Nothing`; `printRawCommandAndArgsAndEnv verbosity path args Nothing` is more readable. The original code made this distinction on purpose.

There's also a subtle functionality difference: `printRawCommandAndArgsAndEnv ... Nothing` prints the empty environment, while your version doesn't.