THRIFT-3498 C++ library assumes optional function pthread_attr_setschedpolicy is available
Client: C++
Patch: Simon South

PosixThreadFactory.cpp: Test for availability of optional
pthread_attr_setschedpolicy function before including in source code

This closes #754
diff --git a/lib/cpp/src/thrift/concurrency/PosixThreadFactory.cpp b/lib/cpp/src/thrift/concurrency/PosixThreadFactory.cpp
index 47c5034..05a3c02 100644
--- a/lib/cpp/src/thrift/concurrency/PosixThreadFactory.cpp
+++ b/lib/cpp/src/thrift/concurrency/PosixThreadFactory.cpp
@@ -124,9 +124,11 @@
     policy_ = PosixThreadFactory::OTHER;
 #endif
 
+#if _POSIX_THREAD_PRIORITY_SCHEDULING > 0
     if (pthread_attr_setschedpolicy(&thread_attr, policy_) != 0) {
       throw SystemResourceException("pthread_attr_setschedpolicy failed");
     }
+#endif
 
     struct sched_param sched_param;
     sched_param.sched_priority = priority_;