Silence warning in -Asserts build

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159635 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index 7fbe0d0..e439c12 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -1737,6 +1737,7 @@
   Target.resize(CharByteWidth * (Source.size() + 1));
   char* ResultPtr = &Target[0];
   bool success = ConvertUTF8toWide(CharByteWidth, Source, ResultPtr);
+  (void)success;
   assert(success);
   Target.resize(ResultPtr - &Target[0]);
 }