Currently clang and nvcc use c++14 as default std for C++.
gcc 11 even uses c++17 as default std for C++. However,
clang uses c++98 as default std for CUDA/HIP.
As c++14 has been well adopted and became default for
clang, it seems reasonable to use c++14 as default std
for CUDA/HIP.
Reviewed by: Artem Belevich
Differential Revision: https://reviews.llvm.org/D103221
Yaxun (Sam) Liu