ROCm/HIP specfic fixes + updates

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

   Updating the HIPCC implementation half so that it can declared as a __shared__ variable


2. Eigen/src/Core/util/Macros.h, Eigen/src/Core/util/Memory.h

   introducing a EIGEN_USE_STD(func) macro that calls
   - std::func be default
   - ::func when eigen is being compiled with HIPCC

   This change was requested in the previous HIP PR
   (https://bitbucket.org/eigen/eigen/pull-requests/518/pr-with-hip-specific-fixes-for-the-eigen/diff)


3. unsupported/Eigen/CXX11/src/Tensor/TensorDeviceThreadPool.h

   Removing EIGEN_DEVICE_FUNC attribute from pure virtual methods as it is not supported by HIPCC


4. unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h

   Disabling the template specializations of InnerMostDimReducer as they run into HIPCC link errors

1 files changed, 1 insertions, 1 deletions

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h b/unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h
index bda114751..50fa0cb2e 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h
@@ -195,6 +195,7 @@ struct InnerMostDimReducer<Self, Op, true, false> {
   }
 };
 
+#if !defined(EIGEN_HIPCC) 
 static const int kLeafSize = 1024;
 
 template <typename Self, typename Op>
@@ -218,7 +219,6 @@ struct InnerMostDimReducer<Self, Op, false, true> {
   }
 };
 
-#if !defined(EIGEN_HIPCC) 
 template <typename Self, typename Op>
 struct InnerMostDimReducer<Self, Op, true, true> {
   static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE typename Self::CoeffReturnType