[gn build] Port 84b7bcf

Author: llvmgnsyncbot

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

@@ -17,6 +17,7 @@ unittest("AMDGPUTests") {
   include_dirs = [ "//llvm/lib/Target/AMDGPU" ]
   sources = [
     "AMDGPUUnitTests.cpp",
+    "CSETest.cpp",
     "DwarfRegMappings.cpp",
     "ExecMayBeModifiedBeforeAnyUse.cpp",
     "PALMetadata.cpp",