[ORC] Switch to shared_ptr ownership for AsynchronousSymbolQueries.

Queries need to stay alive until each owner has set the values they are
responsible for.

llvm-svn: 325179
diff --git a/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp b/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp
index 59f7414..872efea 100644
--- a/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp
@@ -19,8 +19,9 @@
   return Symbols;
 }
 
-SymbolNameSet NullResolver::lookup(AsynchronousSymbolQuery &Query,
-                                   SymbolNameSet Symbols) {
+SymbolNameSet
+NullResolver::lookup(std::shared_ptr<AsynchronousSymbolQuery> Query,
+                     SymbolNameSet Symbols) {
   assert(Symbols.empty() && "Null resolver: Symbols must be empty");
   return Symbols;
 }