Introduce experimental Wayland backend

This patch introduces a new backend that enables GLFW applications to
run on Wayland. For now, only output is supported (windowed and
fullscreen). Pointer cursor management, input devices, clipboard etc are
not supported yet.

There are some concepts that can not be supported, more specifically
glfwSetWindowPos, glfwGetWindowPos and glfwSetCursorPos, as they are not
supported by Wayland.

This patch also changes the time and joystick implementations used by the
X11 backend to be shared between the Wayland backend and the X11 backend.

src/x11_platform.h

@@ -62,6 +62,12 @@
  #error "No supported context creation API selected"
 #endif
 
+#define _GLFW_UNIX_TIME_CONTEXT _glfw.x11.timer
+#include "unix_time.h"
+
+#define _GLFW_LINUX_JOYSTICK_CONTEXT _glfw.x11.joystick
+#include "linux_joystick.h"
+
 #define _GLFW_PLATFORM_WINDOW_STATE         _GLFWwindowX11  x11
 #define _GLFW_PLATFORM_LIBRARY_WINDOW_STATE _GLFWlibraryX11 x11
 #define _GLFW_PLATFORM_MONITOR_STATE        _GLFWmonitorX11 x11
@@ -199,11 +205,7 @@ typedef struct _GLFWlibraryX11
         int         exposure;
     } saver;
 
-    struct {
-        GLboolean   monotonic;
-        double      resolution;
-        uint64_t    base;
-    } timer;
+    _GLFWtimeUNIX   timer;
 
     struct {
         char*       string;
@@ -213,15 +215,7 @@ typedef struct _GLFWlibraryX11
         Window      source;
     } xdnd;
 
-    struct {
-        int         present;
-        int         fd;
-        float*      axes;
-        int         axisCount;
-        unsigned char* buttons;
-        int         buttonCount;
-        char*       name;
-    } joystick[GLFW_JOYSTICK_LAST + 1];
+    _GLFWjoystickLinux joystick;
 
 } _GLFWlibraryX11;
 
@@ -251,9 +245,6 @@ typedef struct _GLFWcursorX11
 // Prototypes for platform specific internal functions
 //========================================================================
 
-// Time
-void _glfwInitTimer(void);
-
 // Gamma
 void _glfwInitGammaRamp(void);
 
@@ -261,10 +252,6 @@ void _glfwInitGammaRamp(void);
 GLboolean _glfwSetVideoMode(_GLFWmonitor* monitor, const GLFWvidmode* desired);
 void _glfwRestoreVideoMode(_GLFWmonitor* monitor);
 
-// Joystick input
-void _glfwInitJoysticks(void);
-void _glfwTerminateJoysticks(void);
-
 // Unicode support
 long _glfwKeySym2Unicode(KeySym keysym);