Meta: Add gn build rules for LibGL and its dependencies

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

@@ -0,0 +1,21 @@
+shared_library("LibGPU") {
+  output_name = "gpu"
+  include_dirs = [ "//Userland/Libraries" ]
+  sources = [
+    "Driver.cpp",
+    "Image.cpp",
+  ]
+  deps = [
+    "//AK",
+    "//Userland/Libraries/LibCore",
+  ]
+
+  # FIXME: express this dependency properly to avoid cycles
+  #    we want to make sure that LibSoftGPU is built when LibGPU is needed
+  #data_deps = [ "//Userland/Libraries/LibSoftGPU" ]
+  if (current_os == "serenity") {
+    #data_deps += [ "//Userland/Libraries/LibVirtGPU" ]
+  } else if (current_os == "linux") {
+    libs = [ "dl" ]
+  }
+}