For Blender 4.0 only, 3.3 and 3.6 keep using the older Xcode version.
The new linker in Xcode 15 gives many warnings due to duplicated
libraries, generated by CMake to resolve circular dependencies. For now
use the old linker to silence these warnings.
Remove legacy flags for libc++, this is the default for a long time and
generates warnings with the new linker.
Reason for upgrade is to take advantage of MetalRT curve support.
Pull Request: https://projects.blender.org/blender/blender/pulls/110243
d387ef224f