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>

gpu/headless/headless_darwin.go

@@ -10,10 +10,10 @@ import (
 )
 
 /*
-#cgo CFLAGS: -Werror -Wno-deprecated-declarations -fmodules -fobjc-arc -x objective-c
-#cgo LDFLAGS: -framework CoreGraphics
+#cgo CFLAGS: -Werror -Wno-deprecated-declarations -fobjc-arc -x objective-c
+#cgo LDFLAGS: -framework CoreGraphics -framework Metal -framework Foundation
 
-@import Metal;
+#import <Metal/Metal.h>
 
 static CFTypeRef createDevice(void) {
 	@autoreleasepool {

gpu/internal/metal/metal_darwin.go

@@ -13,10 +13,8 @@ import (
 )
 
 /*
-#cgo CFLAGS: -Werror -xobjective-c -fmodules -fobjc-arc
-#cgo LDFLAGS: -framework CoreGraphics
-
-@import Metal;
+#cgo CFLAGS: -Werror -xobjective-c -fobjc-arc
+#cgo LDFLAGS: -framework CoreGraphics -framework Metal -framework Foundation
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <Metal/Metal.h>