Fix issue with absolute path with Python 3.13 on Windows

With Python 3.13 on Windows, `os.path.isabs()` no longer returns `True`
for a path that starts with a slash. Thus, when the argument to
`_make_relative()` is an absolute path, the return value starts with a
slash on Python 3.13 and does not start with a slash on older Python
versions. This causes the extension module build directory to be
calculated incorrectly with Python 3.13 on Windows.

Fix this by ensuring that the return value does not start with a slash.

distutils/ccompiler.py

@@ -989,7 +989,8 @@ def _make_relative(base):
         # Chop off the drive
         no_drive = os.path.splitdrive(base)[1]
         # If abs, chop off leading /
-        return no_drive[os.path.isabs(no_drive) :]
+        is_abs = os.path.isabs(no_drive) or sys.platform == 'win32' and (no_drive.startswith('/') or no_drive.startswith('\\'))
+        return no_drive[is_abs:]
 
     def shared_object_filename(self, basename, strip_dir=False, output_dir=''):
         assert output_dir is not None