Added std:: qualifier to find() invocation

Iterator of std::vector may be implemented as a raw pointer. In
this case ADL does not find the find() function in the std namespace.
For example, this is the case with STDCXX implementation of vector.

Patch by Konstantin Tokarev.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189733 91177308-0d34-0410-b5e6-96231b3b80d8