adding a null backend for nfd

lib/nfd/build.zig

@@ -31,15 +31,19 @@ pub fn build(b: *std.Build) void {
         });
         mod.linkSystemLibrary("ole32", .{});
     } else if (target.result.os.tag == .linux) {
+        // mod.addCSourceFile(.{
+        //     .file = b.path("src/nfd_gtk.c"),
+        //     .flags = &.{},
+        // });
         mod.addCSourceFile(.{
-            .file = b.path("src/nfd_gtk.c"),
+            .file = b.path("src/nfd_null.c"),
             .flags = &.{},
         });
-        mod.linkSystemLibrary("gdk-3", .{});
-        mod.linkSystemLibrary("atk-1.0", .{});
-        mod.linkSystemLibrary("gtk-3", .{});
-        mod.linkSystemLibrary("glib-2.0", .{});
-        mod.linkSystemLibrary("gobject-2.0", .{});
+        // mod.linkSystemLibrary("gdk-3", .{});
+        // mod.linkSystemLibrary("atk-1.0", .{});
+        // mod.linkSystemLibrary("gtk-3", .{});
+        // mod.linkSystemLibrary("glib-2.0", .{});
+        // mod.linkSystemLibrary("gobject-2.0", .{});
     }
 
     const p2dep = b.dependency("p2", .{ .target = target, .optimize = optimize });

lib/nfd/src/nfd_null.c

@@ -0,0 +1,42 @@
+/*
+  Native File Dialog
+
+  http://www.frogtoss.com/labs
+*/
+
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+#include "nfd.h"
+#include "nfd_common.h"
+
+
+const char INIT_FAIL_MSG[] = "gtk_init_check failed to initilaize GTK+";
+
+nfdresult_t NFD_OpenDialog( const nfdchar_t *filterList,
+                            const nfdchar_t *defaultPath,
+                            nfdchar_t **outPath )
+{    
+    return NFD_CANCEL;
+}
+
+
+nfdresult_t NFD_OpenDialogMultiple( const nfdchar_t *filterList,
+                                    const nfdchar_t *defaultPath,
+                                    nfdpathset_t *outPaths )
+{
+    return NFD_CANCEL;
+}
+
+nfdresult_t NFD_SaveDialog( const nfdchar_t *filterList,
+                            const nfdchar_t *defaultPath,
+                            nfdchar_t **outPath )
+{
+    return NFD_CANCEL;
+}
+
+nfdresult_t NFD_PickFolder(const nfdchar_t *defaultPath,
+    nfdchar_t **outPath)
+{
+    return NFD_CANCEL;
+}