all: add support for macOS to flake.nix

The Nix version of the macOS toolchain has difficulties compiling
Objective-C modules; disable modules instead of figuring out why.
It also doesn't include any frameworks automatically; add them explicitly.

While here, move suppression of OpenGL deprecation to a GL-specific
file.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/os_darwin.m

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-@import Dispatch;
-@import Foundation;
+#import <Dispatch/Dispatch.h>
+#import <Foundation/Foundation.h>
 
 #include "_cgo_export.h"