Collapsed revision (based on pull request PR-325)

* Support compiling without IO streams

Add the preprocessor definition EIGEN_NO_IO which, if defined,
disables all use of the IO streams part of the standard library.

Eigen/src/Core/arch/GPU/Half.h

@@ -607,10 +607,12 @@ EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC half (max)(const half& a, const half& b) {
 #endif
 }
 
+#ifndef EIGEN_NO_IO
 EIGEN_ALWAYS_INLINE std::ostream& operator << (std::ostream& os, const half& v) {
   os << static_cast<float>(v);
   return os;
 }
+#endif
 
 } // end namespace half_impl