bpo-30860: Consolidate stateful runtime globals. (#3397)

* group the (stateful) runtime globals into various topical structs
* consolidate the topical structs under a single top-level _PyRuntimeState struct
* add a check-c-globals.py script that helps identify runtime globals

Other globals are excluded (see globals.txt and check-c-globals.py).
diff --git a/PC/pyconfig.h b/PC/pyconfig.h
index 0da6841..4e25fbd 100644
--- a/PC/pyconfig.h
+++ b/PC/pyconfig.h
@@ -278,18 +278,20 @@
 /* For an MSVC DLL, we can nominate the .lib files used by extensions */
 #ifdef MS_COREDLL
 #       ifndef Py_BUILD_CORE /* not building the core - must be an ext */
-#               if defined(_MSC_VER)
-                        /* So MSVC users need not specify the .lib file in
-                        their Makefile (other compilers are generally
-                        taken care of by distutils.) */
-#                       if defined(_DEBUG)
-#                               pragma comment(lib,"python37_d.lib")
-#                       elif defined(Py_LIMITED_API)
-#                               pragma comment(lib,"python3.lib")
-#                       else
-#                               pragma comment(lib,"python37.lib")
-#                       endif /* _DEBUG */
-#               endif /* _MSC_VER */
+#               ifndef Py_BUILD_CORE_MODULE
+#                       if defined(_MSC_VER)
+                                /* So MSVC users need not specify the .lib
+                                file in their Makefile (other compilers are
+                                generally taken care of by distutils.) */
+#                               if defined(_DEBUG)
+#                                       pragma comment(lib,"python37_d.lib")
+#                               elif defined(Py_LIMITED_API)
+#                                       pragma comment(lib,"python3.lib")
+#                               else
+#                                       pragma comment(lib,"python37.lib")
+#                               endif /* _DEBUG */
+#                       endif /* _MSC_VER */
+#               endif /* Py_BUILD_CORE_MODULE */
 #       endif /* Py_BUILD_CORE */
 #endif /* MS_COREDLL */