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

base/threading/platform_thread_posix.cc

Index: base/threading/platform_thread_posix.cc
diff --git a/base/threading/platform_thread_posix.cc b/base/threading/platform_thread_posix.cc
index 9a6a2bb999c4fe80adc83f874a0a08ea7b72116c..d9ee1ff7af57a8a7f6f8f647bc0961e229965514 100644
--- a/base/threading/platform_thread_posix.cc
+++ b/base/threading/platform_thread_posix.cc
@@ -144,7 +144,9 @@ PlatformThreadId PlatformThread::CurrentId() {
 #elif defined(OS_NACL) && !defined(__GLIBC__)
   // Pointers are 32-bits in NaCl.
   return reinterpret_cast<int32_t>(pthread_self());
-#elif defined(OS_POSIX)
+#elif defined(OS_POSIX) && defined(OS_AIX)
+  return pthread_self();
+#elif defined(OS_POSIX) && !defined(OS_AIX)
   return reinterpret_cast<int64_t>(pthread_self());
 #endif
 }