Silence UBSan warnings on Cinder's GC hooks

Summary:
UBSan is picky about calling functions through technically-incompatible
pointers, since this is technically undefined behaviour. It's not a useful
warning in this case (we're calling it with a different pointer type, but
PyMem_RawFree takes a void* anyway) and we don't want to pay the cost of an
extra indirection just to avoid this technically-undefined behaviour, so
just silence it.

Reviewed By: alexmalyshev

Differential Revision: D114423869

fbshipit-source-id: 8a664022830b89c38c932ab8f946b54bf671d8ad

Author: Yhg1s

Python/gc.c

@@ -2135,6 +2135,13 @@ _Ci_PyGC_GetImpl(GCState *gc_state)
 
 static void
 _Ci_PyGCImpl_Fini(GCState *gc_state)
+#if defined(__has_feature)
+#  if __has_feature(undefined_behavior_sanitizer)
+        // Silence the UBSan warning about calling PyMem_RawFree through an
+        // incorrect pointer type.
+        __attribute__((no_sanitize("function")))
+#  endif
+#endif
 {
     _Ci_PyGCImplListNode *node = Ci_find_gc_impl_node(gc_state);
     assert(node != NULL);