Fix project-local build flags being ignored.

I noticed that running ‘cabal install’ with two separate sets of dynamic /
static build flags (e.g. one with none, and one with ‘--enable-shared
--enable-executable-dynamic --disable-library-vanilla’) produced packages with
the same hash, instead of different hashes.

After debugging this issue I found that this command (with no explicit cabal
project file) was resulting in these build configuration flags being ignored,
because in ProjectPlanning.hs, the sdist was not considered a local package, so
the (non-shared) local-package-only configuration was being dropped.

This fix ensures that these command-line arguments properly make it through to
where they belong in cases like this.

Additionally, adjust the ‘style’ attribute in plan.json so that globally
installed packages are designated as global even if they are local to the
project.  (Without this adjustment to ‘style2str’, the T5782Diamond test fails,
because it looks up ‘dist-dirs’ in plan.json, where ‘dist-dirs’ is absent from
the JSON.)

Finally, take into account elabDynExe and configDynExe to provide GHC with
‘-dynamic’ appropriately rather than going about it with static linking.