ART: Use __ANDROID__ instead of HAVE_ANDROID_OS

Use the proper define.

Change-Id: I71e291ac25f5d5f0187ac9b6ef2d6872f19e6085
diff --git a/runtime/mem_map.cc b/runtime/mem_map.cc
index 8df8f96..d9ad7dc 100644
--- a/runtime/mem_map.cc
+++ b/runtime/mem_map.cc
@@ -280,7 +280,7 @@
   ScopedFd fd(-1);
 
 #ifdef USE_ASHMEM
-#ifdef HAVE_ANDROID_OS
+#ifdef __ANDROID__
   const bool use_ashmem = true;
 #else
   // When not on Android ashmem is faked using files in /tmp. Ensure that such files won't