[gn build] Port 96f95c9

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/tools/dsymutil/BUILD.gn

@@ -31,6 +31,7 @@ driver_executable("dsymutil") {
     "MachOUtils.cpp",
     "RelocationMap.cpp",
     "Reproducer.cpp",
+    "SwiftModule.cpp",
     "dsymutil.cpp",
   ]
   if (host_os == "mac") {