Add a missing _VSTD:: before a call to merge. Fixes PR43034. Checked the rest of 'algorithm' looking for unqualified calls. Didn't find any.

llvm-svn: 369463
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 4f41779cca7d9a14fdf273d0dd3e056bbb0d1320
diff --git a/include/algorithm b/include/algorithm
index b90f33c..55ea5eb 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -4382,7 +4382,7 @@
 {
     typedef typename iterator_traits<_InputIterator1>::value_type __v1;
     typedef typename iterator_traits<_InputIterator2>::value_type __v2;
-    return merge(__first1, __last1, __first2, __last2, __result, __less<__v1, __v2>());
+    return _VSTD::merge(__first1, __last1, __first2, __last2, __result, __less<__v1, __v2>());
 }
 
 // inplace_merge