haskell.compiler.ghc8107Binary: tag bindists built using hadrian

Surprisingly, the aarch64-darwin bindist for 8.10.7 was still built
using make.

pkgs/development/compilers/ghc/8.10.7-binary.nix

···
           # instead of `libtinfo.so.*.`
           { nixPackage = ncurses6; fileToCheckFor = "libncursesw.so.6"; }
         ];
+        isHadrian = true;
       };
     };
   };
···
 
     # Our Cabal compiler name
     haskellCompilerName = "ghc-${version}";
+  } // lib.optionalAttrs (binDistUsed.isHadrian or false) {
+    # Normal GHC derivations expose the hadrian derivation used to build them
+    # here. In the case of bindists we just make sure that the attribute exists,
+    # as it is used for checking if a GHC derivation has been built with hadrian.
+    # The isHadrian mechanism will become obsolete with GHCs that use hadrian
+    # exclusively, i.e. 9.6 (and 9.4?).
+    hadrian = null;
   };
 
   meta = rec {