Fix a -Wunused-variable diagnostic.

llvm-svn: 261626
diff --git a/clang/lib/ASTMatchers/ASTMatchersInternal.cpp b/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
index ed48d77..107052e 100644
--- a/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
+++ b/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
@@ -307,8 +307,10 @@
           N.begin(), N.end(),
           [](StringRef Name) { return Name.find("::") == Name.npos; })),
       Names(std::move(N)) {
+#ifndef NDEBUG
   for (StringRef Name : Names)
     assert(!Name.empty());
+#endif
 }
 
 namespace {