add an --hadrian mode to ./validate

When the '--hadrian' flag is passed to the validate script, we use hadrian
to build GHC, package it up in a binary distribution and later on run GHC's
testsuite against the said bindist, which gets installed locally in the process.

Along the way, this commit fixes a typo, an omission (build iserv binaries
before producing the bindist archive) and moves the Makefile that enables
'make install' on those bindists from being a list of strings in the code to
an actual file (it was becoming increasingly annoying to work with).

Finally, the Settings.Builders.Ghc part of this patch is necessary for being
able to use the installed binary distribution, in 'validate'.