Fix a bug in regex_token_iterator's copy constructor. Caught by Bob Wilson.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@199122 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/regex b/include/regex
index f8569f9..b7416f8 100644
--- a/include/regex
+++ b/include/regex
@@ -6288,7 +6288,7 @@
       __subs_(__x.__subs_)
 {
     if (__x.__result_ == &__x.__suffix_)
-        __result_ == &__suffix_;
+        __result_ = &__suffix_;
     else if ( __result_ != nullptr )
         __establish_result ();
 }