[libcxx] [test] Remove nonstandard things and resolve warnings in Xxx_scan tests

Reviewed as https://reviews.llvm.org/D41748

* These tests use function objects from functional, back_inserter from iterator, and equal from algorithm, so add those headers.
* The use of iota targeting vector<unsigned char> with an int parameter triggers warnings on MSVC++ assigning an into a unsigned char&; so change the parameter to unsigned char with a static_cast.
* Avoid naming unary_function in identity here as that is removed in '17. (This also fixes naming _VSTD, _NOEXCEPT_, and other libcxx-isms)
* Change the predicate in the transform tests to add_ten so that problems with multiple application are caught.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@321922 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/numerics/numeric.ops/inclusive.scan/inclusive_scan.pass.cpp

@@ -16,8 +16,11 @@
 //
 
 #include <numeric>
-#include <vector>
+#include <algorithm>
 #include <cassert>
+#include <functional>
+#include <iterator>
+#include <vector>
 
 #include "test_iterators.h"