Fix zig build and minor improvements

- Added zig-pkg directory to gitignore
- Brought min zig version to recent nightly release these improvements
  were completed on
- For linux build, only add rglfw.c if the platform is glfw
- Add a None option to the LinuxDisplayBackend
- Fixed xcode-frameworks dependency and update to using most recent
  commit hash

.gitignore

@@ -118,6 +118,7 @@ GTAGS
 # Zig programming language
 .zig-cache/
 zig-cache/
+zig-pkg/
 zig-out/
 build/
 build-*/