Fix Xcode issues with the premake5 integration

[Ohjurot]

Changelog: Switch to externalincludedirs to fix macos xocde build targets (Fixes #19606 )

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[memsharded]

Thanks for the contribution @Ohjurot

It would be necessary to have first some test that covers this issue, that is, first a test that will be red without the fix, then green with the fix.

There are already some functional premake tests like test_premake_new_generator that can easily serve as a base for adding such a test.