fix(cmake): Correctly report system BLAS in summary

[sincethestudy]

fix(cmake): Correctly report system BLAS in configuration summary

Type

• Bug fix (non-breaking change which fixes an issue): Fixes #
• 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

When configuring Open3D with the USE_SYSTEM_BLAS=ON option, the final configuration summary table incorrectly reported BLAS ..... no. This occurred even though CMake successfully found the system BLAS/LAPACK libraries and configured the build to use them (verified via CMakeCache.txt and the addition of the USE_BLAS preprocessor definition).

This misleading summary output could cause confusion for users building with system BLAS. This change corrects the summary output to accurately reflect the configuration.

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 PR modifies the cmake/Open3DPrintConfigurationSummary.cmake script.

The original logic for printing the status of third-party dependencies checked for the existence of an internal CMake target (Open3D::3rdparty_${dep_lower}). However, when USE_SYSTEM_BLAS=ON, this target (Open3D::3rdparty_blas) is apparently not created, causing the script to fall into the else block and print "no".

The fix adds a specific condition within this else block: if the dependency being checked is "BLAS" and the USE_SYSTEM_BLAS variable is ON, it now correctly prints "yes (system)" instead of "no". This ensures the summary accurately reflects the use of a system-provided BLAS library.

Before:
-- Third-Party Dependencies: -- BLAS .................................... no
After:
-- Third-Party Dependencies: -- BLAS .................................... yes (system)

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.