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

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index d055e705627c96782434537d0157594ff4f6dad0..9fee5904ca7a3a3872f4ca1ded7433ead61a1193 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -69,6 +69,13 @@ if (current_os == "") {
   current_os = target_os
 }
 
+# Checks whether we are running on a Power or z System.
+# This is used many times in multiple files and the four parts
+# of the clause almost always go together.
+# Creating a helper variable vastly improves readability.

[brettw, 2017/04/26 20:07:42]

I think this line:
"Creating a helper variable vastly improves readability."
can just be deleted, I think it's implicit in the above.

[rayb, 2017/04/27 19:29:45]

Done.

+is_power_or_z = current_cpu == "s390x" || current_cpu == "s390" ||

[brettw, 2017/04/26 20:07:42]

If we're going to keep this here, it should be called something like
"current_cpu_is_power_or_z" so it's clear that this applies to the current CPU.

[rayb, 2017/04/27 19:29:45]

Done.

+                current_cpu == "ppc64" || current_cpu == "ppc"
+
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
@@ -135,8 +142,9 @@ declare_args() {
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
-  is_clang = current_os == "mac" || current_os == "ios" ||
-             current_os == "linux" || current_os == "chromeos"
+  is_clang =
+      current_os == "mac" || current_os == "ios" || current_os == "chromeos" ||
+      (current_os == "linux" && !is_power_or_z)
 
   # Allows the path to a custom target toolchain to be injected as a single
   # argument, and set as the default toolchain.
@@ -207,6 +215,8 @@ if (host_toolchain == "") {
     } else {
       host_toolchain = "//build/toolchain/win:$target_cpu"
     }
+  } else if (host_os == "aix") {
+    host_toolchain = "//build/toolchain/aix:$host_cpu"
   } else {
     assert(false, "Unsupported host_os: $host_os")
   }
@@ -242,6 +252,8 @@ if (target_os == "android") {
   } else {
     _default_toolchain = "//build/toolchain/win:$target_cpu"
   }
+} else if (target_os == "aix") {
+  _default_toolchain = "//build/toolchain/aix:$target_cpu"
 } else if (target_os == "winrt_81" || target_os == "winrt_81_phone" ||
            target_os == "winrt_10") {
   _default_toolchain = "//build/toolchain/win:winrt_$target_cpu"
@@ -342,6 +354,15 @@ if (current_os == "win" || current_os == "winrt_81" ||
   is_nacl = false
   is_posix = true
   is_win = false
+} else if (current_os == "aix") {
+  is_android = false
+  is_chromeos = false
+  is_ios = false
+  is_linux = false
+  is_mac = false
+  is_nacl = false
+  is_posix = true
+  is_win = false
 }
 
 # =============================================================================
@@ -370,6 +391,7 @@ if (!is_posix) {
     "*\bposix/*",
   ]
 }
+
 if (!is_win) {
   sources_assignment_filter += [
     "*_win.cc",
@@ -498,11 +520,13 @@ if (current_os == "winrt_81" || current_os == "winrt_81_phone" ||
     current_os == "winrt_10") {
   default_compiler_configs += [ "//build/config/win:target_winrt" ]
 }
+
 if (is_posix) {
-  default_compiler_configs += [
-    "//build/config/gcc:no_exceptions",
-    "//build/config/gcc:symbol_visibility_hidden",
-  ]
+  default_compiler_configs += [ "//build/config/gcc:no_exceptions" ]
+  if (current_os != "aix") {
+    default_compiler_configs +=
+        [ "//build/config/gcc:symbol_visibility_hidden" ]
+  }
 }
 
 if (is_android) {