Non-portable test for SFINAE-friendly std::to_address

[jwakely]

llvm-project/libcxx/test/std/utilities/memory/pointer.conversion/to_address_without_pointer_traits.pass.cpp

Line 56 in 47de55f

static_assert(!is_valid_expansion<TestToAddressCall, int>::value);

This test was added by #65177 which claims to be implementing LWG3545, but that issue only said that pointer_traits should be SFINAE-friendly. It didn't require that to_address should be SFINAE-friendly.

There is a separate (and unresolved) issue about making to_address SFINAE-friendly: LWG4058.

Until LWG4058 is resolved, this test is not portable and relies on a non-standard libc++ extension.