Meta: Add gn rules for dependencies of LibWeb

There's a lot of them, and LibWeb is a massive set of files to build as
well, so let's add these first :^).

Meta/gn/secondary/Userland/Libraries/LibGUI/BUILD.gn

@@ -0,0 +1,23 @@
+# FIXME: Add serenity-only deps and sources
+
+shared_library("LibGUI") {
+  output_name = "gui"
+  include_dirs = [
+    "//Userland/Libraries",
+    "//Userland",
+  ]
+  sources = [
+    "GML/Lexer.cpp",
+    "GML/Parser.cpp",
+    "GML/SyntaxHighlighter.cpp",
+    "Icon.cpp",
+    "Model.cpp",
+    "ModelIndex.cpp",
+  ]
+  deps = [
+    "//AK",
+    "//Userland/Libraries/LibCore",
+    "//Userland/Libraries/LibGfx",
+    "//Userland/Libraries/LibSyntax",
+  ]
+}