ART: Use __ANDROID__ instead of HAVE_ANDROID_OS

Use the proper define.

Change-Id: I71e291ac25f5d5f0187ac9b6ef2d6872f19e6085
diff --git a/runtime/thread_linux.cc b/runtime/thread_linux.cc
index 9d54eba..9563b99 100644
--- a/runtime/thread_linux.cc
+++ b/runtime/thread_linux.cc
@@ -44,7 +44,7 @@
 
 void Thread::SetUpAlternateSignalStack() {
   // Create and set an alternate signal stack.
-#ifdef HAVE_ANDROID_OS
+#ifdef __ANDROID__
   LOG(FATAL) << "Invalid use of alternate signal stack on Android";
 #endif
   stack_t ss;