make gomuks nix package build to a .dylib on macos

linux/nix/pkg/gomuks.nix

@@ -1,9 +1,15 @@
 {
   src,
+  stdenv,
   buildGoModule,
 }:
 
-buildGoModule (finalAttrs: {
+buildGoModule (
+  finalAttrs:
+  let
+    filename = "libgomuks${stdenv.hostPlatform.extensions.sharedLibrary}";
+  in
+  {
     pname = "gomuks-ffi";
     version = "submodule";
 
@@ -16,7 +22,7 @@ buildGoModule (finalAttrs: {
     buildPhase = ''
       runHook preBuild
 
-    go build -buildmode=c-shared -o libgomuks.so -tags goolm,noheic,sqlite_fts5 ./pkg/ffi 
+      go build -buildmode=c-shared -o ${filename} -tags goolm,noheic,sqlite_fts5 ./pkg/ffi 
 
       runHook postBuild
     '';
@@ -24,8 +30,9 @@ buildGoModule (finalAttrs: {
     installPhase = ''
       runHook preInstall
 
-    install -Dm0644 libgomuks.so -t $out/lib
+      install -Dm0644 ${filename} -t $out/lib
 
       runHook postInstall
     '';
-})
+  }
+)