[clang] [CIR][AMDGPU] Route printf in device code through the OpenCL runtime (PR #226435)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Steffen Larsen (steffenlarsen)

<details>
<summary>Changes</summary>

This commit implements CIR support for device-side printf on AMDGPU targets. Previously, any call to printf fell through to a library call, which does not exist on the device, so any kernel calling printf failed to build. For OGCG, the AMDGPU target routes printf calls through the OpenCL printf runtime, which takes the format string and a buffer of appended arguments. This implementation leverages this lowering by first emitting a call to a marker function `__cir_amdgpu_printf` during CIRGen, which is then lowered to the appropriate OpenCL printf runtime call during the LLVM IR lowering, leveraging the existing `llvm::emitAMDGPUPrintfCall` function.

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Full diff: https://github.com/llvm/llvm-project/pull/226435.diff


7 Files Affected:

- (modified) clang/include/clang/CIR/LowerToLLVM.h (+6) 
- (modified) clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp (+1-1) 
- (modified) clang/lib/CIR/CodeGen/CIRGenBuiltinAMDGPU.cpp (+39) 
- (modified) clang/lib/CIR/CodeGen/CIRGenFunction.h (+3) 
- (modified) clang/lib/CIR/FrontendAction/CIRGenAction.cpp (+6-2) 
- (modified) clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp (+46) 
- (added) clang/test/CIR/CodeGenHIP/device-printf.hip (+29) 


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https://github.com/llvm/llvm-project/pull/226435