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

build/config/features.gni

 # Copyright 2014 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.
 
 # =============================================
 #   PLEASE DO NOT ADD MORE FLAGS TO THIS FILE
 # =============================================
 #
 # These flags are effectively global. Your feature flag should go near the
 # code it controls. Most of these items are here now because they control
 # legacy global #defines passed to the compiler (now replaced with generated
 # buildflag headers -- see //build/buildflag_header.gni).
 #
 # There is more advice on where to put build flags in the "Build flag" section
 # of //build/config/BUILDCONFIG.gn.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 declare_args() {
   # Enables Native Client support.
-  # Temporarily disable nacl on arm64 linux to get rid of compilation errors.
+  # Temporarily disable nacl on arm64 linux, ppc64 and s390x
+  # to get rid of compilation errors.
   # TODO(mcgrathr): When mipsel-nacl-clang is available, drop the exclusion.
-  enable_nacl = !is_ios && !is_android && !is_chromecast &&
-                current_cpu != "mipsel" && !(is_linux && target_cpu == "arm64")
+  enable_nacl =
+      !is_ios && !is_android && !is_chromecast && current_cpu != "mipsel" &&
+      !(is_linux && target_cpu == "arm64") && !is_power_or_z

[Michael Achenbach, 2017/04/25 14:08:30]

Double-checking: Here's a subtle difference now to the last patchset. Before,
you enumerated also the target_cpu cases while is_power_or_z contains only
current_cpu. IIUC, this would now enable nacl for the host-build (if supported)
when cross-compiling.

[rayb, 2017/04/25 17:28:48]

Form my understanding it's not supported on the host builds when
cross-compiling. But also further changes need to be made to support
cross-compilation using GN on these platforms. So maybe we want that clause to
be added in a separate cl (the one which would contain changes for supporting
cross-compilation).

 
   # Non-SFI is not yet supported on mipsel
   enable_nacl_nonsfi = current_cpu != "mipsel"
 
   # Enables proprietary codecs and demuxers; e.g. H264, AAC, MP3, and MP4.
   # We always build Google Chrome and Chromecast with proprietary codecs.
   #
   # Note: this flag is used by WebRTC which is DEPSed into Chrome. Moving it
   # out of //build will require using the build_overrides directory.
   proprietary_codecs = is_chrome_branded || is_chromecast
@@ skipping 25 matching lines @@
   use_gconf = is_linux && !is_chromeos && !is_chromecast
 
   use_gio = is_linux && !is_chromeos && !is_chromecast
 }
 #
 # =============================================
 #   PLEASE DO NOT ADD MORE FLAGS TO THIS FILE
 # =============================================
 #
 # See comment at the top.