Added self._global_defines check under def _check_if_extra_flags(self):

[jacobfriedman]

Changelog: (Bugfix):

Docs state that the global xcode config will be generated with modification of the above, including exelinkflags and defines, but the _check_if_extra_flags(self) only checks for cflags/cxxflags/ldflags/exelinkflags.

Docs: https://docs.conan.io/2/reference/tools/apple/xcodetoolchain.html#xcodetoolchain-conf

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[czoido]

Hi @jacobfriedman,
Thanks for the contribution, it looks good, I'm adding a test and I think we can merge when the ci passes.

[czoido]

@jacobfriedman I picked your commit, could you please sign the CLA here: conan-io#16429 ?