This patch changes the default macOS x64 linker from the slower legacy
"classic" linker, to the much faster default modern macOS linker. A new
CMake option `WITH_LEGACY_MACOS_X64_LINKER` was also introduced to use
the old linker, set to OFF by default.
As an example from testing on an Intel Macbook, this makes linking time
go from 3min25s to 10s after this change. The reason why the legacy
linker was enforced on x64 in the first place was to silence "platform
load command not found" warnings during linking. Since this behavior is
still desired on the BuildBot, the `WITH_LEGACY_MACOS_X64_LINKER` option
is enforced in the BuildBot macOS configs.
Pull Request: https://projects.blender.org/blender/blender/pulls/134639
8afde59054