Hadrian: fix dynamicGhcPrograms value for the quickest flavour
Quickest does not build anything in a dynamic way, so that
flavour should default to not building "ghc programs" dynamically.
I ran into this problem by building the 'docs' target with quickest,
which failed because at some point we run a haddock command in a
context whose Way is sensitive to dynamicGhcPrograms, and it
started looking for dyn interface files when it shouldn't have.
Test Plan: hadrian/build.sh --flavour=quickest docs
Reviewers: snowleopard, bgamari
Reviewed By: snowleopard
Subscribers: rwbarton, carter
Differential Revision: https://phabricator.haskell.org/D5419