[HIP] Support attribute hip_pinned_shadow

This patch introduces support of hip_pinned_shadow variable for HIP.

A hip_pinned_shadow variable is a global variable with attribute hip_pinned_shadow.
It has external linkage on device side and has no initializer. It has internal
linkage on host side and has initializer or static constructor. It can be accessed
in both device code and host code.

This allows HIP runtime to implement support of HIP texture reference.

Differential Revision: https://reviews.llvm.org/D62738


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@364381 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed