Cocoa: Make timer functions backend independent

This is work towards allowing the Null backend to build for macOS
using the Darwin timer API, without the Cocoa backend being enabled.

src/CMakeLists.txt

@@ -16,10 +16,11 @@ set_target_properties(update_mappings PROPERTIES FOLDER "GLFW3")
 
 if (_GLFW_COCOA)
     target_compile_definitions(glfw PRIVATE _GLFW_COCOA)
-    target_sources(glfw PRIVATE cocoa_platform.h cocoa_joystick.h posix_thread.h
-                                cocoa_init.m cocoa_joystick.m cocoa_monitor.m
-                                cocoa_window.m cocoa_time.c posix_thread.c
-                                nsgl_context.m egl_context.c osmesa_context.c)
+    target_sources(glfw PRIVATE cocoa_platform.h cocoa_joystick.h cocoa_time.h
+                                posix_thread.h cocoa_init.m cocoa_joystick.m
+                                cocoa_monitor.m cocoa_window.m cocoa_time.c
+                                posix_thread.c nsgl_context.m egl_context.c
+                                osmesa_context.c)
 elseif (_GLFW_WIN32)
     target_compile_definitions(glfw PRIVATE _GLFW_WIN32)
     target_sources(glfw PRIVATE win32_platform.h win32_joystick.h win32_time.h

src/cocoa_platform.h

@@ -91,12 +91,12 @@ typedef struct VkMetalSurfaceCreateInfoEXT
 typedef VkResult (APIENTRY *PFN_vkCreateMacOSSurfaceMVK)(VkInstance,const VkMacOSSurfaceCreateInfoMVK*,const VkAllocationCallbacks*,VkSurfaceKHR*);
 typedef VkResult (APIENTRY *PFN_vkCreateMetalSurfaceEXT)(VkInstance,const VkMetalSurfaceCreateInfoEXT*,const VkAllocationCallbacks*,VkSurfaceKHR*);
 
+#include "cocoa_time.h"
 #include "posix_thread.h"
 #include "cocoa_joystick.h"
 
 #define _GLFW_PLATFORM_WINDOW_STATE         _GLFWwindowNS  ns
 #define _GLFW_PLATFORM_LIBRARY_WINDOW_STATE _GLFWlibraryNS ns
-#define _GLFW_PLATFORM_LIBRARY_TIMER_STATE  _GLFWtimerNS   ns
 #define _GLFW_PLATFORM_MONITOR_STATE        _GLFWmonitorNS ns
 #define _GLFW_PLATFORM_CURSOR_STATE         _GLFWcursorNS  ns
 
@@ -204,13 +204,6 @@ typedef struct _GLFWcursorNS
     id              object;
 } _GLFWcursorNS;
 
-// Cocoa-specific global timer data
-//
-typedef struct _GLFWtimerNS
-{
-    uint64_t        frequency;
-} _GLFWtimerNS;
-
 
 void _glfwPollMonitorsNS(void);
 void _glfwSetVideoModeNS(_GLFWmonitor* monitor, const GLFWvidmode* desired);

src/cocoa_time.h

@@ -0,0 +1,35 @@
+//========================================================================
+// GLFW 3.4 macOS - www.glfw.org
+//------------------------------------------------------------------------
+// Copyright (c) 2009-2021 Camilla Löwy <elmindreda@glfw.org>
+//
+// This software is provided 'as-is', without any express or implied
+// warranty. In no event will the authors be held liable for any damages
+// arising from the use of this software.
+//
+// Permission is granted to anyone to use this software for any purpose,
+// including commercial applications, and to alter it and redistribute it
+// freely, subject to the following restrictions:
+//
+// 1. The origin of this software must not be misrepresented; you must not
+//    claim that you wrote the original software. If you use this software
+//    in a product, an acknowledgment in the product documentation would
+//    be appreciated but is not required.
+//
+// 2. Altered source versions must be plainly marked as such, and must not
+//    be misrepresented as being the original software.
+//
+// 3. This notice may not be removed or altered from any source
+//    distribution.
+//
+//========================================================================
+
+#define _GLFW_PLATFORM_LIBRARY_TIMER_STATE  _GLFWtimerNS   ns
+
+// Cocoa-specific global timer data
+//
+typedef struct _GLFWtimerNS
+{
+    uint64_t        frequency;
+} _GLFWtimerNS;
+