[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.

llvm-svn: 321922