[clang] [HIP][SPIRV] Enable the SPIRV backend instead of the translator through an experimental flag. (PR #162282)

[Joseph Huber via cfe-commits]

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+// RUN: %clang -x hip %s --cuda-device-only --offload-arch=amdgcnspirv -use-experimental-spirv-backend -nogpuinc -nogpulib -ccc-print-bindings 2>&1 | FileCheck %s 
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jhuber6 wrote:

Needs a test for the new driver, because if all goes well I'm going to completely delete the old offload driver next release.

https://github.com/llvm/llvm-project/pull/162282