The Interpreter was failing the AtExit UnitTest. This fixes it.

llvm-svn: 11367
diff --git a/llvm/lib/ExecutionEngine/Interpreter/Execution.cpp b/llvm/lib/ExecutionEngine/Interpreter/Execution.cpp
index 57ae621..5379c04 100644
--- a/llvm/lib/ExecutionEngine/Interpreter/Execution.cpp
+++ b/llvm/lib/ExecutionEngine/Interpreter/Execution.cpp
@@ -523,6 +523,10 @@
 //===----------------------------------------------------------------------===//
 
 void Interpreter::exitCalled(GenericValue GV) {
+  // runAtExitHandlers() assumes there are no stack frames, but
+  // if exit() was called, then it had a stack frame. Blow away
+  // the stack before interpreting atexit handlers.
+  ECStack.clear ();
   runAtExitHandlers ();
   exit (GV.IntVal);
 }