nix: fix static build

- the isExecutable patch was broken, remove it
- the ncurses fix was broken, we still need `enableStatic`
- the original error was caused by the new ghc-bignum
  package, which isn't a "proper" Haskell package; we filter
  this out explicitly now

nix/patches/default.nix

@@ -24,6 +24,6 @@
 
   static-haskell-nix-ncurses =
     ./static-haskell-nix-ncurses.patch;
-  static-haskell-nix-isexecutable =
-    ./static-haskell-nix-isexecutable.patch;
+  static-haskell-nix-ghc-bignum =
+    ./static-haskell-nix-ghc-bignum.patch;
 }

nix/patches/static-haskell-nix-ghc-bignum.patch

@@ -0,0 +1,12 @@
+diff --git a/survey/default.nix b/survey/default.nix
+index 70afbbc..28cb0e9 100644
+--- a/survey/default.nix
++++ b/survey/default.nix
+@@ -81,6 +81,7 @@ let
+   # `.override` and the likes).
+   isProperHaskellPackage = val:
+     lib.isDerivation val && # must pass lib.isDerivation
++    val.pname != "ghc-bignum" &&
+     val ? env; # must have an .env key
+
+   # Function that tells us if a given Haskell package has an executable.

nix/patches/static-haskell-nix-ncurses.patch

@@ -7,7 +7,7 @@ index 46d8066..a47f214 100644
                      "--enable-executable-static" # requires `useFixedCabal`
                      # `enableShared` seems to be required to avoid `recompile with -fPIC` errors on some packages.
 -                    "--extra-lib-dirs=${final.ncurses.override { enableStatic = true; enableShared = true; }}/lib"
-+                    "--extra-lib-dirs=${final.ncurses}/lib"
++                    "--extra-lib-dirs=${final.ncurses.override { enableStatic = true; }}/lib"
                    ]
                    # TODO Figure out why this and the below libffi are necessary.
                    #      `working` and `workingStackageExecutables` don't seem to need that,

nix/static-haskell-package.nix

@@ -18,7 +18,7 @@ let
       static-haskell-nix
       [
         patches.static-haskell-nix-ncurses
-        patches.static-haskell-nix-isexecutable
+        patches.static-haskell-nix-ghc-bignum
       ];
 
   patchedNixpkgs =