[libc++] Use std::addressof in std::function::target

This guards against hostile overloads of operator&. Thanks to Peter Dimov
for the report in https://github.com/boostorg/lambda/issues/24.

Differential Revision: https://reviews.llvm.org/D116380

NOKEYCHECK=True
GitOrigin-RevId: e24ddb6027b6495a81c95133cfb6812d6090cd32
3 files changed