[gn build] Port ac0f64f

Author: llvmgnsyncbot

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

@@ -182,6 +182,7 @@ static_library("LLVMAMDGPUCodeGen") {
     "AMDGPURegBankSelect.cpp",
     "AMDGPURegisterBankInfo.cpp",
     "AMDGPURemoveIncompatibleFunctions.cpp",
+    "AMDGPUReserveWWMRegs.cpp",
     "AMDGPUResourceUsageAnalysis.cpp",
     "AMDGPURewriteOutArguments.cpp",
     "AMDGPURewriteUndefForPHI.cpp",