bpo-36876: Re-organize the c-analyzer tool code. (gh-16841)

This is partly a cleanup of the code. It also is preparation for getting the variables from the source (cross-platform) rather than from the symbols.

The change only touches the tool (and its tests).
diff --git a/Tools/c-analyzer/c-globals.py b/Tools/c-analyzer/c-globals.py
index 9afe059..b36b791 100644
--- a/Tools/c-analyzer/c-globals.py
+++ b/Tools/c-analyzer/c-globals.py
@@ -1,6 +1,6 @@
 # This is a script equivalent of running "python -m test.test_c_globals.cg".
 
-from c_globals.__main__ import parse_args, main
+from cpython.__main__ import parse_args, main
 
 
 # This is effectively copied from cg/__main__.py: