ToolInvocation::mapVirtualFile(): Tweak for Win32. Handle the key as native path.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157889 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Tooling/Tooling.cpp b/lib/Tooling/Tooling.cpp
index 50612cb..0c9fa43 100644
--- a/lib/Tooling/Tooling.cpp
+++ b/lib/Tooling/Tooling.cpp
@@ -166,7 +166,9 @@
 }
 
 void ToolInvocation::mapVirtualFile(StringRef FilePath, StringRef Content) {
-  MappedFileContents[FilePath] = Content;
+  SmallString<1024> PathStorage;
+  llvm::sys::path::native(FilePath, PathStorage);
+  MappedFileContents[PathStorage] = Content;
 }
 
 bool ToolInvocation::run() {