Missing _VSTD for merge call

|  |  |
| --- | --- |
| Bugzilla Link | [43034](https://llvm.org/bz43034) |
| Resolution | FIXED |
| Resolved on | Aug 20, 2019 15:24 |
| Version | unspecified |
| OS | All |
| CC | @mclow |

## Extended Description 
Link: https://github.com/llvm-mirror/libcxx/blob/52ba46bf85151fa3cbd444e8d7948a40f28f25ac/include/algorithm#L4385

merge should be probably called with _VSTD:: to avoid ADL issues