[HIP] define __CUDA_ARCH_=1 for amdgcn targets
[HIP] define __CUDA_ARCH_=1 for amdgcn targets

Differential Revision: https://reviews.llvm.org/D45277


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@329420 91177308-0d34-0410-b5e6-96231b3b80d8

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