[gn build] Port 1d286ad

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/Target/AMDGPU/BUILD.gn

@@ -166,6 +166,7 @@ static_library("LLVMAMDGPUCodeGen") {
     "AMDGPUMachineFunction.cpp",
     "AMDGPUMachineModuleInfo.cpp",
     "AMDGPUMacroFusion.cpp",
+    "AMDGPUMarkLastScratchLoad.cpp",
     "AMDGPUOpenCLEnqueuedBlockLowering.cpp",
     "AMDGPUPerfHintAnalysis.cpp",
     "AMDGPUPostLegalizerCombiner.cpp",