[ExpressionParser] Restore removed intance of FileSystem::Resolve while resolving clang resource dir

I committed a change that removed this line, but I meant to restore it
befor committing.

llvm-svn: 356079

lldb/source/Plugins/ExpressionParser/Clang/ClangHost.cpp

@@ -54,6 +54,7 @@ static bool DefaultComputeClangResourceDirectory(FileSpec &lldb_shlib_spec,
   llvm::sys::path::append(clang_dir, relative_path);
   if (!verify || VerifyClangPath(clang_dir)) {
     file_spec.GetDirectory().SetString(clang_dir);
+    FileSystem::Instance().Resolve(file_spec);
     return true;
   }