GN: aix port along with linux_s390x, linux_ppc64 and linux_ppc64le support.

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index 7714190534fc23bd8b879ffb3e119916d6c144d3..8b6a60337db55da852fc8cfc9a003f74370d46cc 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -1212,6 +1212,14 @@ component("base") {
     public_configs = [ ":android_system_libs" ]
   }
 
+  # AIX
+  if (is_aix) {
+    sources += [
+      "base/process/internal_aix.cc",
+      "base/process/internal_aix.h",
+    ]
+  }
+
   # Chromeos.
   if (is_chromeos) {
     sources += [ "power_monitor/power_monitor_device_source_chromeos.cc" ]