Add framework paths from NIX_CFLAGS_COMPILE

[MarcoPolo]

On MacOS, if we're using Nix to supply the frameworks Zig should add the frameworks paths.

Instead we currently emit warning logs (which are a bit noisy). And then potentially fail to build. Users can workaround this by manually parsing the NIX_CFLAGS_COMPILE and adding framework paths manually (basically what this PR does), but it would be great if we did the correct thing here.