For building v8 using gn on aix_ppc64, linux_s390x and linux_ppc64.

build/toolchain/aix/BUILD.gn

Index: build/toolchain/aix/BUILD.gn
diff --git a/build/toolchain/aix/BUILD.gn b/build/toolchain/aix/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..202e59e652cf1421908100e5aeae65786b36d1d6
--- /dev/null
+++ b/build/toolchain/aix/BUILD.gn
@@ -0,0 +1,21 @@
+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/toolchain/gcc_toolchain.gni")
+
+gcc_toolchain("ppc64") {
+  cc = "gcc"
+  cxx = "g++"
+
+  readelf = "readelf"
+  nm = "nm"
+  ar = "ar"
+  ld = cxx
+
+  toolchain_args = {
+    current_cpu = "ppc64"
+    current_os = "aix"
+    is_clang = false
+  }
+}