Teach EHCleanupBlock to deal appropriately with the possibility that there
might not have been an insertion block set at start.  Fixes PR6975.

llvm-svn: 102677
diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index 405df40..a18aaf6 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -696,7 +696,11 @@
 
   // Resume inserting where we started, but put the new cleanup
   // handler in place.
-  CGF.Builder.SetInsertPoint(PreviousInsertionBlock);
+  if (PreviousInsertionBlock)
+    CGF.Builder.SetInsertPoint(PreviousInsertionBlock);
+  else
+    CGF.Builder.ClearInsertionPoint();
+
   if (CGF.Exceptions)
     CGF.setInvokeDest(CleanupHandler);
 }