[gn build] Port 9c9d4b9

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/ExecutionEngine/Orc/Shared/BUILD.gn

@@ -8,5 +8,6 @@ static_library("Shared") {
     "OrcError.cpp",
     "OrcRTBridge.cpp",
     "SimpleRemoteEPCUtils.cpp",
+    "SymbolStringPool.cpp",
   ]
 }