Fix bundled curl and BoringSSL archive grouping

[mstoelzle]

Type

• Bug fix (non-breaking change which fixes an issue): Fixes Bundled static curl and BoringSSL archive grouping is ineffective in Linux source link #7556
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

On Linux shared-library builds with bundled curl and BoringSSL, the current manual linker markers surround the CMake interface target names. CMake expands those targets after the markers, so the generated link command contains an empty group and leaves libcurl.a, libssl.a, and libcrypto.a ungrouped. GNU ld then leaves strong TLS symbols unresolved in libOpen3D.so, and importing the Python package fails.

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

This applies CMake's LINK_GROUP:RESCAN feature to the concrete build-tree archives used by the bundled curl target. It preserves the target's install-interface entries and leaves system curl/OpenSSL and Apple builds unchanged.

The generated Open3D shared-library link command now contains:

-Wl,--start-group
curl/lib/libcurl.a
boringssl/src/ext_boringssl/lib/libssl.a
boringssl/src/ext_boringssl/lib/libcrypto.a
-Wl,--end-group

The separate MKL archive group remains intact.

Validation on Ubuntu x86-64, Open3D b6c5e1963:

• Configured with BUILD_SHARED_LIBS=ON, bundled curl, and bundled BoringSSL.
• Built the complete pip-package target successfully.
• Imported the generated open3d package successfully (0.20.0+b6c5e1963).
• Created open3d.core.Device("CPU:0") successfully.
• nm -D --undefined-only libOpen3D.so.0.20.0 contains no strong OpenSSL/TLS undefined symbols; only BoringSSL's three expected weak memory hooks remain.
• python util/check_style.py --apply passes.

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