Improve algorithm for choosing flags with './Setup configure'

Misc nix-local-build preparation patches

Cabal < 1.12.0 doesn't know about '--enable/disable-executable-dynamic'
or '--enable/disable-library-coverage'.

This is a problem in general, if rare, but it shows up in the
nix-local-build branch more obviously since it always passes all flags,
including defaults (it does this because the defaults should be
determined by the current version, not the older version).

Make the basic dependencyGraph construction function give us just a
Vertex -> UnitId mapping, rather than a full Vertex -> pkg. Then in
InstallPlan we keep that Vertex -> UnitId mapping and add a helper
function that does the additional lookup to give us a Vertex -> pkg
mapping. It's clearer this way, especially in the case of lookup errors.

This is easier to understand now that the canonical data vs the cached
graph is clarified. We only store the main data, the cached info is
reconstructed on deserialisation.

This is to clarify the lazy caching strategy we use for the fields for
the Graph (forward and reverse deps, and associated mappings).
Reorder the fields, and mark non-lazy fields as strict. Make
construction go via a smart constructor that fills in the cached fields.

Useful for reporting dir/file names in user interface code, e.g. in
notices and error messages.

Required by later nix-local-build branch patches.

Required by later nix-local-build branch patches.

Add Binary instances for many types

So we can use them in binary cache files.

Also relax version constraints on binary to work with binary-0.5.*,
which requires that we expose Distribution.Compat.Binary from Cabal.

D.Compat.Binary provides the Gerics support that we need to be able to
derive instances when using binary-0.5. It's useful to be able to use
binary-0.5 since that's the version bundled with older ghc versions.

remove duplicate LANGUAGE DeriveFoldable, minor improvements

Cabal previously tried all flag combinations, which was very slow.  The new
algorithm assigns one flag at a time, and backtracks when a flag introduces a
dependency that is unavailable.

The new algorithm handles the Buildable field by adding an extra conditional at
the top level of each component that represents the condition for which the
component is buildable.  Since all dependencies go under the "then" branch, they
are only required when a flag choice makes the component buildable.  The buildable
logic is taken from the cabal-install dependency solver.

This commit also changes the error message that is shown when dependencies are
missing.  Previously, Cabal printed the shortest list of missing dependencies
from a single flag assignment.  Now it takes the union of all dependencies that
caused it to backtrack when trying different combinations of flags, which
requires less searching.

Fix space leak in ./Setup configure

redundant map after fold

See https://github.com/haskell/cabal/issues/3003#issuecomment-174492371

It uses 'build-type: Simple' now.

Fixes #3003.

Fix bug in solver independent goals.

Add some more backwards-compatibility functions, fixes #3068.

Missing parentheses caused the solver to skip preferring linked packages with
the use of --reorder-goals.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Also rename it to '--documentation'. Note that the shorthand still works.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>