Can't reliably detect missing profiling versions of preinstalled packages

[r0ml]

When ghc list --simple says that some packages are preinstalled, we assume that the profiling versions are also installed. This is a bold assumption.

Currently users would need to either install the profiling versions, or uninstall the package entirely, to build the full platform.

[mzero]

the new build doesn't look at "preinstalled" packages at all
it uses the GHC bindist, which, I suppose, might not have profiling libs... which would be reasonable to detect in hptool