[bug] XcodeToolchain's conan_global_flags.xcconfig not flagged to save if _global_defines is populated

[jacobfriedman]

Describe the bug

Changelog: (Bugfix):

Docs state that the global xcode config will be generated with modification of the _global_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

How to reproduce it

Attempt to modify _global_defines and conan_global_flags.xcconfig will not be created.

Fix:
jacobfriedman#1

[czoido]

Hi @jacobfriedman,
Thanks a lot for reporting. Indeed it seems a bug.
Adding this to be fixed in the 2.5.0 release.

[memsharded]

Closed by #16429 for 2.5