[gn build] Port 0c1bb4f

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/TableGen/BUILD.gn

@@ -2,6 +2,7 @@ static_library("TableGen") {
   output_name = "LLVMTableGen"
   deps = [ "//llvm/lib/Support" ]
   sources = [
+    "DetailedRecordsBackend.cpp",
     "Error.cpp",
     "JSONBackend.cpp",
     "Main.cpp",