[ORC] Remove COFFPlatform::DylibsToPreload. NFC.

DylibsToPreload is only used in the constructor. This patch makes it a local
variable.
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/COFFPlatform.h b/llvm/include/llvm/ExecutionEngine/Orc/COFFPlatform.h
index cebab0f..acfefbc 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/COFFPlatform.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/COFFPlatform.h
@@ -202,8 +202,6 @@
 
   DenseMap<JITDylib *, SymbolLookupSet> RegisteredInitSymbols;
 
-  std::set<std::string> DylibsToPreload;
-
   std::mutex PlatformMutex;
 };
 
diff --git a/llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp b/llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp
index 9ff12b2..ce04062 100644
--- a/llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/COFFPlatform.cpp
@@ -401,6 +401,7 @@
   }
   VCRuntimeBootstrap = std::move(*VCRT);
 
+  std::set<std::string> DylibsToPreload;
   for (auto &Lib : OrcRuntimeGenerator->getImportedDynamicLibraries())
     DylibsToPreload.insert(Lib);