in other words, has anything been done to the compiler to allow for a ‘special case’ the STL needed to work?
No.
It was all implemented as ‘pure’ C++ code, using the magic of templates.
There has been some work done to compilers to improve the STL (I’m thinking about various optimisations) but otherwise, no, you could write the entire STL if you really wanted. Some people did – STLPort is an implementation that didn’t have the backing of any compiler manufacturer.