add a bunch of missing prototypes to tests


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@93072 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/block-labels.c b/test/Sema/block-labels.c
index af364b4..353a570 100644
--- a/test/Sema/block-labels.c
+++ b/test/Sema/block-labels.c
@@ -1,5 +1,7 @@
 // RUN: %clang_cc1 %s -verify -fblocks -fsyntax-only
 
+void xx();
+
 int a() { 
   A:if (1) xx();
   return ^{A:return 1;}();