Readd lost "undef BUILTIN" to fix the build.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154837 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/Basic/BuiltinsHexagon.def b/include/clang/Basic/BuiltinsHexagon.def
index 34d080f..c57f9b9 100644
--- a/include/clang/Basic/BuiltinsHexagon.def
+++ b/include/clang/Basic/BuiltinsHexagon.def
@@ -857,3 +857,5 @@
 BUILTIN(__builtin_HEXAGON_S2_ct1p,"iLLi","")
 BUILTIN(__builtin_HEXAGON_S2_interleave,"LLiLLi","")
 BUILTIN(__builtin_HEXAGON_S2_deinterleave,"LLiLLi","")
+
+#undef BUILTIN