[cherry-pick][swift/release/6.0] [lldb][DataFormatter] unordered_map: account for new libc++ __hash_node layout

[Michael137]

Since D101206 (ba79fb2e1ff7130cde02fbbd325f0f96f8a522ca) the __hash_node::__value_ member is wrapped in an anonymous union. ValueObject::GetChildMemberWithName doesn't see through the union.

This patch accounts for this possible new layout by getting a handle to the union before doing the by-name __value_ lookup.

(cherry picked from commit 7493d45)

[Michael137]

@swift-ci test

[adrian-prantl]

Is the fact that this commit came without a test also the reason why we missed it? ;-)

[Michael137]

Is the fact that this commit came without a test also the reason why we missed it? ;-)

Hehe seems like it. The current tests will always only test the layout of the freshly built libc++. One thing we could do is run all the formatters against the system SDK and also the newly built libc++ (this wouldn't of course be bullet-proof). Another option is to follow what we did for std::string, where we hardcode all the different formats that ever existed for std::string in the tests, and make sure the formatters work for those (https://github.com/llvm/llvm-project/blob/72e2e4f7dc682fa3f6eda9f3cfbd20a8ffaac4e4/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string/simulator/main.cpp).