[Backport 2.24-maintenance] addToStore(): Evaluate on the main stack

[edolstra]

Motivation

We observed a segfault on macOS with Nix 2.24.3 in BDW-GC inside a coroutine:

  * frame #0: 0x0000000100542f49 libgc.1.dylib`GC_push_all_stack + 201
    frame #1: 0x0000000100537a6b libgc.1.dylib`GC_default_push_other_roots + 1115
    frame #2: 0x000000010053dbe5 libgc.1.dylib`GC_push_roots + 2181
...
    frame #11: 0x0000000100801846 libnixexpr.dylib`nix::EvalState::allocBindings(unsigned long) + 102
...
    frame #64: 0x0000000100ed2708 libnixutil.dylib`nix::SourceAccessor::dumpPath(nix::CanonPath const&, nix::Sink&, std::__1::function<bool (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)>&) + 216
    frame #65: 0x0000000100f63578 libnixutil.dylib`void boost::context::detail::fiber_entry<boost::context::detail::fiber_record<boost::context::fiber, nix::VirtualStackAllocator, boost::coroutines2::detail::pull_coroutine<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>::control_block::control_block<nix::VirtualStackAllocator, nix::sinkToSource(std::__1::function<void (nix::Sink&)>, std::__1::function<void ()>)::SinkToSource::read(char*, unsigned long)::'lambda'(boost::coroutines2::detail::push_coroutine<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>&)>(boost::context::preallocated, nix::VirtualStackAllocator&&, nix::sinkToSource(std::__1::function<void (nix::Sink&)>, std::__1::function<void ()>)::SinkToSource::read(char*, unsigned long)::'lambda'(boost::coroutines2::detail::push_coroutine<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>&)&&)::'lambda'(boost::context::fiber&&)>>(boost::context::detail::transfer_t) + 216
    frame #66: 0x000000010040da2f libboost_context.dylib`trampoline + 3

Switching to Nix master made the segfault go away, so it's likely that #11152 fixed this issue.

Context

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