[VL] Refine CMAKE_CXX_FLAGS setting logic

[Yohahaha]

What changes were proposed in this pull request?

Modify CMAKE_CXX_FLAGS generation logic for each native module, and make it clearly to see all the CMAKE_CXX_FLAGS.

[github-actions[bot]]

Thanks for opening a pull request!

Could you open an issue for this pull request on Github Issues?

https://github.com/apache/incubator-gluten/issues

Then could you also rename commit message and pull request title in the following format?

[GLUTEN-${ISSUES_ID}][COMPONENT]feat/fix: ${detailed message}

See also:

• Other pull requests

[FelixYBW]

Is there impact to build process?

[Yohahaha]

Is there impact to build process?

no changes, just a little refactor.

[Yohahaha]

@marin-ma @PHILO-HE please help take a look, thank you!