[clang] [clang] Handle instantiated members to determine visibility (PR #136128)

[Andrew Savonichev via cfe-commits]

asavonic wrote:

Libcxx tests failed. I'll check them tomorrow.
```
Failed Tests (15):
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/extents/assert.conversion.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/extents/assert.ctor_from_array.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/extents/assert.ctor_from_integral.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/extents/assert.ctor_from_span.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/extents/assert.obs.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_left/assert.conversion.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_left/assert.ctor.extents.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_left/assert.ctor.layout_right.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_left/assert.ctor.layout_stride.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_right/assert.conversion.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_right/assert.ctor.extents.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_right/assert.ctor.layout_left.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_right/assert.ctor.layout_stride.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_stride/assert.ctor.extents_array.pass.cpp
  llvm-libc++-shared.cfg.in :: libcxx/containers/views/mdspan/layout_stride/assert.ctor.extents_span.pass.cpp
```

```
# | /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-bt7k7-1/llvm-project/github-pull-requests/libcxx/test/libcxx/containers/views/mdspan/extents/assert.conversion.pass.cpp:39:29: error: declaration of 'dynamic_extent' must be imported from module 'std.span.fwd' before it is required
# |    39 |   constexpr size_t D = std::dynamic_extent;
# |       |                             ^
# | /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-bt7k7-1/llvm-project/github-pull-requests/build/runtimes/runtimes-bins/libcxx/test-suite-install/include/c++/v1/__fwd/span.h:28:25: note: declaration here is not visible
# |    28 | inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
# |       |                         ^
# | 1 error generated.
```


https://github.com/llvm/llvm-project/pull/136128