ART: Use __ANDROID__ instead of HAVE_ANDROID_OS

Use the proper define.

Change-Id: I71e291ac25f5d5f0187ac9b6ef2d6872f19e6085
diff --git a/sigchainlib/sigchain.cc b/sigchainlib/sigchain.cc
index 8e9d421..c984b17 100644
--- a/sigchainlib/sigchain.cc
+++ b/sigchainlib/sigchain.cc
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#ifdef HAVE_ANDROID_OS
+#ifdef __ANDROID__
 #include <android/log.h>
 #else
 #include <stdarg.h>
@@ -103,7 +103,7 @@
   va_list ap;
   va_start(ap, format);
   vsnprintf(buf, sizeof(buf), format, ap);
-#ifdef HAVE_ANDROID_OS
+#ifdef __ANDROID__
   __android_log_write(ANDROID_LOG_ERROR, "libsigchain", buf);
 #else
   std::cout << buf << "\n";