Win32: Make timer functions backend independent

This is work towards allowing the Null backend to build for Windows
using the Win32 timer API, without the Win32 backend being enabled.

src/CMakeLists.txt

@@ -22,10 +22,11 @@ if (_GLFW_COCOA)
                                 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_thread.h
+    target_sources(glfw PRIVATE win32_platform.h win32_joystick.h win32_time.h
-                                win32_init.c win32_joystick.c win32_monitor.c
+                                win32_thread.h win32_init.c win32_joystick.c
-                                win32_time.c win32_thread.c win32_window.c
+                                win32_monitor.c win32_time.c win32_thread.c
-                                wgl_context.c egl_context.c osmesa_context.c)
+                                win32_window.c wgl_context.c egl_context.c
+                                osmesa_context.c)
 elseif (_GLFW_X11)
     target_compile_definitions(glfw PRIVATE _GLFW_X11)
     target_sources(glfw PRIVATE x11_platform.h xkb_unicode.h posix_time.h

src/win32_platform.h

@@ -352,6 +352,7 @@ typedef struct VkWin32SurfaceCreateInfoKHR
 typedef VkResult (APIENTRY *PFN_vkCreateWin32SurfaceKHR)(VkInstance,const VkWin32SurfaceCreateInfoKHR*,const VkAllocationCallbacks*,VkSurfaceKHR*);
 typedef VkBool32 (APIENTRY *PFN_vkGetPhysicalDeviceWin32PresentationSupportKHR)(VkPhysicalDevice,uint32_t);
 
+#include "win32_time.h"
 #include "win32_thread.h"
 #include "win32_joystick.h"
 
@@ -361,7 +362,6 @@ typedef VkBool32 (APIENTRY *PFN_vkGetPhysicalDeviceWin32PresentationSupportKHR)(
 
 #define _GLFW_PLATFORM_WINDOW_STATE         _GLFWwindowWin32  win32
 #define _GLFW_PLATFORM_LIBRARY_WINDOW_STATE _GLFWlibraryWin32 win32
-#define _GLFW_PLATFORM_LIBRARY_TIMER_STATE  _GLFWtimerWin32   win32
 #define _GLFW_PLATFORM_MONITOR_STATE        _GLFWmonitorWin32 win32
 #define _GLFW_PLATFORM_CURSOR_STATE         _GLFWcursorWin32  win32
 
@@ -518,13 +518,6 @@ typedef struct _GLFWcursorWin32
     HCURSOR             handle;
 } _GLFWcursorWin32;
 
-// Win32-specific global timer data
-//
-typedef struct _GLFWtimerWin32
-{
-    uint64_t            frequency;
-} _GLFWtimerWin32;
-
 
 GLFWbool _glfwRegisterWindowClassWin32(void);
 void _glfwUnregisterWindowClassWin32(void);

src/win32_time.h

@@ -0,0 +1,38 @@
+//========================================================================
+// GLFW 3.4 Win32 - www.glfw.org
+//------------------------------------------------------------------------
+// Copyright (c) 2002-2006 Marcus Geelnard
+// Copyright (c) 2006-2017 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.
+//
+//========================================================================
+
+#include <windows.h>
+
+#define _GLFW_PLATFORM_LIBRARY_TIMER_STATE  _GLFWtimerWin32   win32
+
+// Win32-specific global timer data
+//
+typedef struct _GLFWtimerWin32
+{
+    uint64_t            frequency;
+} _GLFWtimerWin32;
+