Add scons with_x86_64h option on macOS

[Ivorforce]

This adds an x86_64h slice, which can lead to improved performance (at the cost of binary size). It will be selected automatically on all post-2013 macs, if compiled. Pre 2013 macs will use the current x86_64 slice.

See https://github.com/godotengine/godot-proposals/issues/11150 for details about this feature.

The x86_64h slice is compiled alongside the x86_64 slice and is fully and transparently compatible with x86_64 godot. Therefore, we don't need to wait for any progress on the godot front to add this feature.

❯ scons arch=x86_64 dev_build=yes with_x86_64h=yes
...

❯ lipo -info project/bin/libgdexample.macos.template_debug.framework/libgdexample.macos.template_debug
Architectures in the fat file: project/bin/libgdexample.macos.template_debug.framework/libgdexample.macos.template_debug are: x86_64 x86_64h

godot-cpp/test x86_64h-slice-option ≡
❯ GODOT=/Applications/Godot4.4-dev4.app/Contents/MacOS/Godot  ./run-tests.sh
Godot Engine v4.4.dev4.official.36e6207bb - https://godotengine.org


 ==== TESTS FINISHED ====

   PASSES: 124
   FAILURES: 0

 ******** PASSED ********

grep: repetition-operator operand invalid

Removing the slice to see if x86_64h can be selected:

godot-cpp/test x86_64h-slice-option ≡
❯ lipo -remove x86_64 project/bin/libgdexample.macos.template_debug.framework/libgdexample.macos.template_debug -output project/bin/libgdexample.macos.template_debug.framework/libgdexample.macos.template_debug

❯ lipo -info project/bin/libgdexample.macos.template_debug.framework/libgdexample.macos.template_debug
Architectures in the fat file: project/bin/libgdexample.macos.template_debug.framework/libgdexample.macos.template_debug are: x86_64h

godot-cpp/test x86_64h-slice-option ≡
❯ GODOT=/Applications/Godot4.4-dev4.app/Contents/MacOS/Godot  ./run-tests.sh
Godot Engine v4.4.dev4.official.36e6207bb - https://godotengine.org


 ==== TESTS FINISHED ====

   PASSES: 124
   FAILURES: 0

 ******** PASSED ********

grep: repetition-operator operand invalid

godot-cpp/test x86_64h-slice-option ≡

[Ivorforce]

It may be nice to have an option to build only for x86_64h (instead of x86_64), to kill compatibility to older macs by choice. I opted not to add that because gdextensions should probably be fully compatible to everything godot is compatible with.

[Ivorforce]

However, I'm not totally sure about including this in godot-cpp. How commonly would this be used?

Realistically, probably not a lot. The reason I proposed it anyway is that, for Intel macOS targets, it's an "instantaneous performance upgrade" at no development cost, though it does make the binary twice as large. Exposing it through SCons would 'expose' developers to it, since it's not a very well known trick. I guess with Apple phasing out Intel, it's not all that relevant.