usewayland follow GLFW_BUILD_WAYLAND instead of _GLFW_WAYLAND

[duarm]

After glfw/glfw@56a4cb0 , glfw can now use the GLFW_BUILD_X11 and GLFW_BUILD_WAYLAND defines to include x11/wayland support, both backends can now coexist and be dinamically selected when opening a window. We should do that instead of an if-else compiling only one backend

https://github.com/glfw/glfw/blob/46cebb5081820418f2a20f3e90b07f9b1bd44b42/src/CMakeLists.txt#L51

if (GLFW_BUILD_WAYLAND)
    target_compile_definitions(glfw PRIVATE _GLFW_WAYLAND)
    target_sources(glfw PRIVATE wl_platform.h xkb_unicode.h wl_init.c
                                wl_monitor.c wl_window.c xkb_unicode.c)
endif()

[duarm]

With the release of 3.8, both are now included by default