Reverting std lib is in std:: namespace and using .h versions instead

The previous patch is [incompatible with Android](https://github.com/leethomason/tinyxml2/commit/7fbefab95d7785dc5fed8251891157aea4229c16#commitcomment-2389688), I changed the method for my goal (compatibility with Borland C++).
I revert the previous patch + I add a test on Borland C++ compiler