Roll GN, clang and libc++ to match chromium revisions

Updates the GN binary and the libc++, libc++abi and libunwind
to match the most recent versions rolled into chrome.
Has no effect on the Android tree builds.
The new GN version seem to have stricter checks on include
paths. This CL therefore fixes the GN files to make deps
explicit and keep gn check happy (they all seem to make sense).

Change-Id: I0930b957099da78c8d5ebfebfd8dd387638496fd
diff --git a/gn/ipc_library.gni b/gn/ipc_library.gni
index 3d57ee6..5d0df92 100644
--- a/gn/ipc_library.gni
+++ b/gn/ipc_library.gni
@@ -27,15 +27,14 @@
 
     generate_python = false
     generator_plugin_label =
-        perfetto_root_path + "src/ipc/protoc_plugin:ipc_plugin"
+        "$perfetto_root_path/src/ipc/protoc_plugin:ipc_plugin"
     generator_plugin_suffix = ".ipc"
     deps = [
-      "${perfetto_root_path}src/ipc",
+      "$perfetto_root_path/src/ipc",
     ]
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
-
     forward_variables_from(invoker,
                            [
                              "defines",