Fix test failing on RHEL8

On that platform, libc is called libc-2.28.so, not libc.so. Instead, the test searches for libffi.so, which is a dependency of ctypes

Author: WardBrian

Lib/test/test_ctypes/test_dllist.py

@@ -11,11 +11,14 @@
 APPLE = sys.platform in {"darwin", "ios", "tvos", "watchos"}
 
 if WINDOWS:
-    SYSTEM_LIBRARY = 'KERNEL32.DLL'
+    KNOWN_LIBRARY = 'KERNEL32.DLL'
 elif APPLE:
-    SYSTEM_LIBRARY = 'libSystem.B.dylib'
+    KNOWN_LIBRARY = 'libSystem.B.dylib'
 else:
-    SYSTEM_LIBRARY = 'libc.so'
+    # trickier than it seems, because libc may not be present
+    # on musl systems, and sometimes goes by different names.
+    # However, ctypes itself loads libffi
+    KNOWN_LIBRARY = 'libffi.so'
 
 class ListSharedLibraries(unittest.TestCase):
 
@@ -24,7 +27,7 @@ def test_lists_system(self):
 
         self.assertIsNotNone(dlls)
         self.assertGreater(len(dlls), 0, f'loaded={dlls}')
-        self.assertTrue(any(SYSTEM_LIBRARY in dll for dll in dlls), f'loaded={dlls}')
+        self.assertTrue(any(KNOWN_LIBRARY in dll for dll in dlls), f'loaded={dlls}')
 
 
     def test_lists_updates(self):