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

build/config/features.gni

Index: build/config/features.gni
diff --git a/build/config/features.gni b/build/config/features.gni
index d143dac4b89ce082835f225866a0e9f164ccc019..7bb8b6397cb30b9953c63fa32cbcb440b5f70ab6 100644
--- a/build/config/features.gni
+++ b/build/config/features.gni
@@ -22,10 +22,12 @@ if (is_android) {
 
 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"