Fix the type of 1<<31 integer constants.

Shifting into the sign bit is technically undefined behavior. No known
compiler exploits it though.

llvm-svn: 342909
diff --git a/clang/lib/CodeGen/CGBlocks.h b/clang/lib/CodeGen/CGBlocks.h
index c802948..3f9fc16 100644
--- a/clang/lib/CodeGen/CGBlocks.h
+++ b/clang/lib/CodeGen/CGBlocks.h
@@ -60,7 +60,7 @@
   BLOCK_IS_GLOBAL =         (1 << 28),
   BLOCK_USE_STRET =         (1 << 29),
   BLOCK_HAS_SIGNATURE  =    (1 << 30),
-  BLOCK_HAS_EXTENDED_LAYOUT = (1 << 31)
+  BLOCK_HAS_EXTENDED_LAYOUT = (1u << 31)
 };
 class BlockFlags {
   uint32_t flags;