Export the Py_FrozenMain() function: fix a Python 3.9.0 regression.
Python 3.9 uses -fvisibility=hidden and the function was not exported
explicitly and so not exported.
Add also Py_FrozenMain to the stable ABI on Windows.
It was moved out of the limited API in 7d95e40721.
This change re-enables it from 3.10, to avoid generating invalid extension modules for earlier versions.
Remove the global _Py_CheckRecursionLimit variable: it has been
replaced by ceval.recursion_limit of the PyInterpreterState
structure.
There is no need to keep the variable for the stable ABI, since
Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() were not usable
in Python 3.8 and older: these macros accessed PyThreadState members,
whereas the PyThreadState structure is opaque in the limited C API.
Use linker comment #pragma and preprocessor for re-exporting stable
API functions and variables.
Module definition file, custom build targets and entry point code
become unnecessary and can be removed.
This change also fixes missing _PyErr_BadInternalCall export on x86.
