gh-111506: Error if the limited API is used in free-threaded build (#117762)

Issue a build time error if both `Py_LIMITED_API` and `Py_GIL_DISABLED`
are defined.

Author: colesbury

Include/Python.h

@@ -45,6 +45,11 @@
 #  endif
 #endif
 
+// gh-111506: The free-threaded build is not compatible with the limited API
+// or the stable ABI.
+#if defined(Py_LIMITED_API) && defined(Py_GIL_DISABLED)
+#  error "The limited API is not currently supported in the free-threaded build"
+#endif
 
 // Include Python header files
 #include "pyport.h"