Adding support for llvm.eh.begincatch and llvm.eh.endcatch intrinsics and beginning the documentation of native Windows exception handling.

Differential Revision: http://reviews.llvm.org/D7398

llvm-svn: 228733
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 0074e14..d60c695 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5670,6 +5670,9 @@
 
     return nullptr;
   }
+  case Intrinsic::eh_begincatch:
+  case Intrinsic::eh_endcatch:
+    llvm_unreachable("begin/end catch intrinsics not lowered in codegen");
   }
 }