[ORC] Add note to call endSession to assertion messages.

The most likely cause of these assertions is a failure to call endSession. The
new message should clients spot the issue more easily.

Author: lhames

llvm/lib/ExecutionEngine/Orc/LinkGraphLinkingLayer.cpp

@@ -499,7 +499,10 @@ LinkGraphLinkingLayer::LinkGraphLinkingLayer(
 }
 
 LinkGraphLinkingLayer::~LinkGraphLinkingLayer() {
-  assert(Allocs.empty() && "Layer destroyed with resources still attached");
+  assert(Allocs.empty() &&
+         "Layer destroyed with resources still attached "
+         "(ExecutionSession::endSession() must be called prior to "
+         "destruction)");
   getExecutionSession().deregisterResourceManager(*this);
 }
 

llvm/lib/ExecutionEngine/Orc/RTDyldObjectLinkingLayer.cpp

@@ -88,7 +88,10 @@ RTDyldObjectLinkingLayer::RTDyldObjectLinkingLayer(
 }
 
 RTDyldObjectLinkingLayer::~RTDyldObjectLinkingLayer() {
-  assert(MemMgrs.empty() && "Layer destroyed with resources still attached");
+  assert(MemMgrs.empty() &&
+         "Layer destroyed with resources still attached"
+         "(ExecutionSession::endSession() must be called prior to "
+         "destruction)");
 }
 
 void RTDyldObjectLinkingLayer::emit(