Fix gcc -Wreturn-type warnings after r326307.

llvm-svn: 326355
diff --git a/clang/lib/CodeGen/CGBlocks.cpp b/clang/lib/CodeGen/CGBlocks.cpp
index 7bd6176..5c35e09 100644
--- a/clang/lib/CodeGen/CGBlocks.cpp
+++ b/clang/lib/CodeGen/CGBlocks.cpp
@@ -1595,6 +1595,7 @@
     return std::make_pair(BlockCaptureEntityKind::None, BlockFieldFlags());
   }
   }
+  llvm_unreachable("after exhaustive PrimitiveCopyKind switch");
 }
 
 /// Find the set of block captures that need to be explicitly copied or destroy.
@@ -1797,6 +1798,7 @@
     return std::make_pair(BlockCaptureEntityKind::None, BlockFieldFlags());
   }
   }
+  llvm_unreachable("after exhaustive DestructionKind switch");
 }
 
 /// Generate the destroy-helper function for a block closure object: