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

build/toolchain/linux/BUILD.gn

Index: build/toolchain/linux/BUILD.gn
diff --git a/build/toolchain/linux/BUILD.gn b/build/toolchain/linux/BUILD.gn
index 3be5c36bca692d526d0bdba10a3b0c036922aca5..5b7689f9f2d31f796a990252e16430fb3d08ad12 100644
--- a/build/toolchain/linux/BUILD.gn
+++ b/build/toolchain/linux/BUILD.gn
@@ -170,3 +170,35 @@ gcc_toolchain("mipsel") {
     use_goma = false
   }
 }
+
+gcc_toolchain("s390x") {
+  cc = "gcc"
+  cxx = "g++"
+
+  readelf = "readelf"
+  nm = "nm"
+  ar = "ar"
+  ld = cxx
+
+  toolchain_args = {
+    current_cpu = "s390x"
+    current_os = "linux"
+    is_clang = false
+  }
+}
+
+gcc_toolchain("ppc64") {
+  cc = "gcc"
+  cxx = "g++"
+
+  readelf = "readelf"
+  nm = "nm"
+  ar = "ar"
+  ld = cxx
+
+  toolchain_args = {
+    current_cpu = "ppc64"
+    current_os = "linux"
+    is_clang = false
+  }
+}