modules: FindGLFW.cmake should prefer absolute includes.

It's not like with SDL where we can't use <SDL2/SDL.h> due to macOS
packaged shipped without the SDL2 include directory.

This was just a bad copypaste from the FindSDL2.cmake module, probably.

modules/FindGLFW.cmake

@@ -43,8 +43,7 @@ find_library(GLFW_LIBRARY NAMES glfw glfw3)
 
 # Include dir
 find_path(GLFW_INCLUDE_DIR
-    NAMES glfw3.h
-    PATH_SUFFIXES GLFW)
+    NAMES GLFW/glfw3.h)
 
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args("GLFW" DEFAULT_MSG

src/Magnum/Platform/GlfwApplication.h

@@ -42,7 +42,7 @@
 /* We must include our own GL headers first to avoid conflicts */
 #include "Magnum/OpenGL.h"
 
-#include <glfw3.h>
+#include <GLFW/glfw3.h>
 
 namespace Magnum { namespace Platform {