[gn build] Port 71e8021

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/Target/X86/BUILD.gn

@@ -98,6 +98,7 @@ static_library("LLVMX86CodeGen") {
     "X86ISelDAGToDAG.cpp",
     "X86ISelLowering.cpp",
     "X86IndirectBranchTracking.cpp",
+    "X86IndirectThunks.cpp",
     "X86InsertPrefetch.cpp",
     "X86InsertWait.cpp",
     "X86InstrFMA3Info.cpp",
@@ -114,7 +115,6 @@ static_library("LLVMX86CodeGen") {
     "X86PartialReduction.cpp",
     "X86RegisterBankInfo.cpp",
     "X86RegisterInfo.cpp",
-    "X86RetpolineThunks.cpp",
     "X86SelectionDAGInfo.cpp",
     "X86ShuffleDecodeConstantPool.cpp",
     "X86SpeculativeLoadHardening.cpp",