Add support for building the Dart VM for Android OS.

runtime/platform/thread_android.cc

Index: runtime/platform/thread_android.cc
diff --git a/runtime/platform/thread_linux.cc b/runtime/platform/thread_android.cc
similarity index 99%
copy from runtime/platform/thread_linux.cc
copy to runtime/platform/thread_android.cc
index 30e8dcdb34272374b954a7cb08138d3230d51ce4..ae47d49e13874968676213d31f76953ccd345267 100644
--- a/runtime/platform/thread_linux.cc
+++ b/runtime/platform/thread_android.cc
@@ -211,8 +211,11 @@ Monitor::Monitor() {
   result = pthread_condattr_init(&cond_attr);
   VALIDATE_PTHREAD_RESULT(result);
 
+#if 0
+  // This API is not available on Android.

[cshapiro, 2012/08/07 20:56:54]

It is, but only through the non-standard name  pthread_cond_timedwait_monotonic.

I think you should remove this code and update the code for Monitor::Wait to use
pthread_cond_timedwait_monotonic.

[jackpal, 2012/08/07 21:43:26]

Done.

   result = pthread_condattr_setclock(&cond_attr, CLOCK_MONOTONIC);
   VALIDATE_PTHREAD_RESULT(result);
+#endif
 
   result = pthread_cond_init(data_.cond(), &cond_attr);
   VALIDATE_PTHREAD_RESULT(result);