[gn build] Port b4a62b1

Author: llvmgnsyncbot

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

@@ -231,6 +231,7 @@ static_library("LLVMAMDGPUCodeGen") {
     "SILowerControlFlow.cpp",
     "SILowerI1Copies.cpp",
     "SILowerSGPRSpills.cpp",
+    "SILowerWWMCopies.cpp",
     "SIMachineFunctionInfo.cpp",
     "SIMachineScheduler.cpp",
     "SIMemoryLegalizer.cpp",