Parse the variables in a type signature in the order given (Trac #8945)

This is just making the parser behave more sensibly, and return
the list [x,y,z] from the signature
   x,y,z :: Int
rathe than [x,z,y] as now.

Turns out that the other use of sig_vars *did* do the right
thing already.

compiler/parser/Parser.y.pp

@@ -1041,7 +1041,7 @@ sigtypedoc :: { LHsType RdrName }       -- Always a HsForAllTy
         : ctypedoc                      { L1 (mkImplicitHsForAllTy (noLoc []) $1) }
         -- Wrap an Implicit forall if there isn't one there already
 
-sig_vars :: { Located [Located RdrName] }
+sig_vars :: { Located [Located RdrName] }  -- Returned in reversed order
          : sig_vars ',' var             { LL ($3 : unLoc $1) }
          | var                          { L1 [$1] }
 
@@ -1423,7 +1423,7 @@ sigdecl :: { Located (OrdList (LHsDecl RdrName)) }
                         {% do s <- checkValSig $1 $3
                         ; return (LL $ unitOL (LL $ SigD s)) }
         | var ',' sig_vars '::' sigtypedoc
-                                { LL $ toOL [ LL $ SigD (TypeSig ($1 : unLoc $3) $5) ] }
+                                { LL $ toOL [ LL $ SigD (TypeSig ($1 : reverse (unLoc $3)) $5) ] }
         | infix prec ops        { LL $ toOL [ LL $ SigD (FixSig (FixitySig n (Fixity $2 (unLoc $1))))
                                              | n <- unLoc $3 ] }
         | '{-# INLINE' activation qvar '#-}'