Avoid using pthread_condattr_setclock on Android.

The pthread_condattr_setclock is available only since
Android 5.0 and API level 21.

src/libstd/sys/unix/condvar.rs

@@ -30,10 +30,10 @@ impl Condvar {
         Condvar { inner: UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER) }
     }
 
-    #[cfg(any(target_os = "macos", target_os = "ios"))]
+    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android"))]
     pub unsafe fn init(&mut self) {}
 
-    #[cfg(not(any(target_os = "macos", target_os = "ios")))]
+    #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "android")))]
     pub unsafe fn init(&mut self) {
         use mem;
         let mut attr: libc::pthread_condattr_t = mem::uninitialized();
@@ -69,7 +69,7 @@ impl Condvar {
     // where we configure condition variable to use monotonic clock (instead of
     // default system clock). This approach avoids all problems that result
     // from changes made to the system time.
-    #[cfg(not(any(target_os = "macos", target_os = "ios")))]
+    #[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "android")))]
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
         use mem;
 
@@ -99,7 +99,7 @@ impl Condvar {
     // This implementation is modeled after libcxx's condition_variable
     // https://github.com/llvm-mirror/libcxx/blob/release_35/src/condition_variable.cpp#L46
     // https://github.com/llvm-mirror/libcxx/blob/release_35/include/__mutex_base#L367
-    #[cfg(any(target_os = "macos", target_os = "ios"))]
+    #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android"))]
     pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
         use ptr;
         use time::Instant;