Update `Cabal` to 1.18.1.3 release

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Major Call Arity rework

This patch improves the call arity analysis in various ways.

Most importantly, it enriches the analysis result information so that
when looking at a call, we do not have to make a random choice about
what side we want to take the information from. Instead we can combine
the results in a way that does not lose valuable information.

To do so, besides the incoming arities, we store remember "what can be
called with what", i.e. an undirected graph between the (interesting)
free variables of an expression. Of course it makes combining the
results a bit more tricky (especially mutual recursion), but still
doable.

The actually implemation of the graph structure is abstractly put away
in a module of its own (UnVarGraph.hs)

The implementation is geared towards efficiently representing the graphs
that we need (which can contain large complete and large complete
bipartite graphs, which would be huge in other representations). If
someone feels like designing data structures: There is surely some
speed-up to be obtained by improving that data structure.

Additionally, the analysis now takes into account that if a RHS stays a
thunk, then its calls happen only once, even if the variables the RHS is
bound to is evaluated multiple times, or is part of a recursive group.
Typos in comments
Add some debug tracing
Make the demand on a binder compatible with type (fixes Trac #8569)

Because of GADTs and casts we were getting binders whose
demand annotation was more deeply nested than made sense
for its type.

See Note [Trimming a demand to a type], in Demand.lhs,
which I reproduce here:

   Note [Trimming a demand to a type]
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Consider this:

     f :: a -> Bool
     f x = case ... of
             A g1 -> case (x |> g1) of (p,q) -> ...
             B    -> error "urk"

   where A,B are the constructors of a GADT.  We'll get a U(U,U) demand
   on x from the A branch, but that's a stupid demand for x itself, which
   has type 'a'. Indeed we get ASSERTs going off (notably in
   splitUseProdDmd, Trac #8569).

   Bottom line: we really don't want to have a binder whose demand is more
   deeply-nested than its type.  There are various ways to tackle this.
   When processing (x |> g1), we could "trim" the incoming demand U(U,U)
   to match x's type.  But I'm currently doing so just at the moment when
   we pin a demand on a binder, in DmdAnal.findBndrDmd.
Attach the right location to pattern synonym error message (fixes Trac #8841)
Test for Trac #8841 now works
Trac #8569 fixed
Test #8851.
Run testcase for 8124 only with threaded ways
Make sync-all handle all github protocols correctly

This fixes #8824.
Make -XDeriveFunctor more generous about non-last arguments (Trac #8678)

When deriving Functor, Foldable, Traversable, we need only look at the
way that the last type argument is treated.  It's fine for there to
be existentials etc, provided they don't affect the last type argument.

See Note [Check that the type variable is truly universal] in TcDeriv.
Fix the treatment of lexically scoped kind variables (Trac #8856)

The issue here is described in Note [Binding scoped type variables] in
TcPat.  When implementing this fix I was able to make things quite a
bit simpler:
 * The type variables in a type signature now never unify
   with each other, and so can be straightfoward skolems.
 * We only need the SigTv stuff for signatures in patterns,
   and for kind variables.
Test Trac #8856
Also allow http://github.com (#8824)
Treat '_' as a meta variable
Add extra constraints wildcard to TypeSig and TcSigInfo
Update README & add demo
Add named wildcards (syntax and renamer)
Desugar named wildcards to meta vars