Add run-time context creation API selection Fixes #145.

diff --git a/src/wl_platform.h b/src/wl_platform.h
index d75c025..221108e 100644
--- a/src/wl_platform.h
+++ b/src/wl_platform.h

@@ -49,12 +49,7 @@
 #include "posix_time.h"
 #include "linux_joystick.h"
 #include "xkb_unicode.h"
-
-#if defined(_GLFW_EGL)
- #include "egl_context.h"
-#else
- #error "The Wayland backend depends on EGL platform support"
-#endif
+#include "egl_context.h"
 
 #include "wayland-relative-pointer-unstable-v1-client-protocol.h"
 #include "wayland-pointer-constraints-unstable-v1-client-protocol.h"
@@ -71,6 +66,9 @@
 #define _GLFW_PLATFORM_MONITOR_STATE        _GLFWmonitorWayland wl
 #define _GLFW_PLATFORM_CURSOR_STATE         _GLFWcursorWayland  wl
 
+#define _GLFW_PLATFORM_CONTEXT_STATE
+#define _GLFW_PLATFORM_LIBRARY_CONTEXT_STATE
+
 
 // Wayland-specific video mode data
 //