Fix Windows build for t-strings

[AA-Turner]

This fixes the build for Windows such that _templatelib is importable, and makes the Unix configuration consistent with other builtin modules.

I still get an assertion error, though:

>>> spam = 'ham'
>>> t'{spam}'
Assertion failed: tstate->current_frame == NULL || tstate->current_frame->stackpointer != NULL, file ...\Objects\object.c, line 3017

[lysnikolaou]

Thanks a lot @AA-Turner! I wouldn't really be able to do the Windows stuff myself.