Fix crash in hphp

The AnalysisResult for systemlib.php was allowed to go out of
scope, taking the FileScope with it, causing us to crash when
trying to flatten systemlib traits.

hphp/compiler/builtin_symbols.cpp

@@ -91,6 +91,7 @@ StringToClassScopePtrMap BuiltinSymbols::s_classes;
 VariableTablePtr BuiltinSymbols::s_variables;
 ConstantTablePtr BuiltinSymbols::s_constants;
 StringToTypePtrMap BuiltinSymbols::s_superGlobals;
+AnalysisResultPtr BuiltinSymbols::s_systemAr;
 void *BuiltinSymbols::s_handle_main = nullptr;
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -329,7 +330,7 @@ bool BuiltinSymbols::Load(AnalysisResultPtr ar, bool extOnly /* = false */) {
 
   // parse all PHP files under system/classes
   if (!extOnly) {
-    ar = AnalysisResultPtr(new AnalysisResult());
+    s_systemAr = ar = AnalysisResultPtr(new AnalysisResult());
     ar->loadBuiltinFunctions();
     string slib = get_systemlib();
 

hphp/compiler/builtin_symbols.h

@@ -65,6 +65,7 @@ public:
   static StringToClassScopePtrMap s_classes;
   static VariableTablePtr s_variables;
   static ConstantTablePtr s_constants;
+  static AnalysisResultPtr s_systemAr;
 
   static const char *const GlobalNames[];
   static int NumGlobalNames();

hphp/test/slow/traits/sys_trait.php

@@ -0,0 +1,9 @@
+<?php
+class X { use IterableTrait; }
+function test() {
+  $x = new X;
+  var_dump($x->view());
+}
+test();
+
+

hphp/test/slow/traits/sys_trait.php.expect

@@ -0,0 +1,2 @@
+object(X)#1 (0) {
+}