When I try and compile on 64-bit (build.macos64x64/squeak.cog.spur; macOS High Sierra 10.13.6; clang --version: Apple LLVM version 7.0.0 (clang-700.1.76) Target: x86_64-apple-darwin17.7.0) I get the following error message:
../../platforms/iOS/vm/OSX/sqSqueakOSXMetalView.m:79:17: error: ARC forbids Objective-C objects in struct
that line is the "texture" declaration in
typedef struct ExtraLayer { id<MTLTexture> texture; int x, y; int w, h; } ExtraLayer;