[chore] Hide symbols by default for extension build

[tqchen]

This PR hides the symbols by default for extension build. not strictly necessary good to avoid potential symbol conflict

[gemini-code-assist]

Summary of Changes

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This pull request enhances the robustness and isolation of the torch_c_dlpack extension by explicitly managing symbol visibility during its build and loading phases. By hiding symbols by default and enforcing local symbol loading, the changes aim to prevent potential symbol conflicts with other shared libraries, leading to a more stable and predictable runtime environment for the extension.

Highlights

• Symbol Visibility: The build process for the torch_c_dlpack extension now explicitly hides symbols by default by adding the -fvisibility=hidden flag to the compiler options. This helps prevent symbol conflicts when loading multiple shared libraries.
• CDLL Loading Mode: The ctypes.CDLL calls used to load the torch_c_dlpack extension are now explicitly configured to use ctypes.RTLD_LOCAL. This ensures that symbols from the loaded library are not made available to other libraries loaded later, further reducing potential symbol clashes.

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[gemini-code-assist]

Code Review

This pull request aims to improve the extension build process by hiding symbols by default and explicitly setting the CDLL loading mode. While these are good practices, the implementation for setting the CDLL loading mode using ctypes.RTLD_LOCAL is not cross-platform and will cause an AttributeError on Windows. I've provided critical feedback with suggestions to fix this issue in both affected files.