[analyzer] Don't use the address of a temporary CFGElement.

GCC destroys temporary objects more aggressively than clang, so this
results in incorrect behavior when compiling GCC Release builds.

We could avoid this issue under C++11 by preventing getAs from being
called when 'this' is an rvalue:

  template<class ElemTy> const ElemTy *getAs() const & { ... }
  template<class ElemTy> const ElemTy *getAs() const && = delete;

Unfortunately, we do not have compatibility macros for this behavior yet.

This will hopefully fix PR13760 and PR13762.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@163402 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Core/CoreEngine.cpp b/lib/StaticAnalyzer/Core/CoreEngine.cpp
index 8b7eeef..84d2cc6 100644
--- a/lib/StaticAnalyzer/Core/CoreEngine.cpp
+++ b/lib/StaticAnalyzer/Core/CoreEngine.cpp
@@ -514,7 +514,8 @@
-  const CFGStmt *CS = (*Block)[Idx].getAs<CFGStmt>();
+  CFGElement Elem = (*Block)[Idx];
+  const CFGStmt *CS = Elem.getAs<CFGStmt>();
   const Stmt *St = CS ? CS->getStmt() : 0;
   PostStmt Loc(St, N->getLocationContext());