wayland: Support building with static wayland/libdecor (fix libsdl-or…

…g#4543)

When wayland is not dynamically linked (--enable-wayland-shared=no),
libdecor is always also statically linked (it's treated as part of
Wayland in SDL_waylanddyn.{c,h} and SDL_waylandsym.h). However, it
doesn't include libdecor.h unless SDL_VIDEO_DRIVER_WAYLAND_DYNAMIC is
set, so it fails to build at all unless Wayland is dynamically loaded.

This is @sezero's suggested fix of simply moving the libdecor.h include
outside the #ifdef SDL_VIDEO_DRIVER_WAYLAND_DYNAMIC block:
libsdl-org#4543 (comment)

Note that this doesn't fix any of the underlying issues of libdecor
being treated as part of wayland, it just fixes the build.

src/video/wayland/SDL_waylanddyn.h

@@ -53,6 +53,11 @@ enum libdecor_window_state;
 #include "xkbcommon/xkbcommon.h"
 #include "xkbcommon/xkbcommon-compose.h"
 
+#ifdef HAVE_LIBDECOR_H
+/* Must be included before our defines */
+#include <libdecor.h>
+#endif
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -115,8 +120,6 @@ void SDL_WAYLAND_UnloadSymbols(void);
 #define wl_data_device_manager_interface (*WAYLAND_wl_data_device_manager_interface)
 
 #ifdef HAVE_LIBDECOR_H
-/* Must be included before our defines */
-#include <libdecor.h>
 
 #define libdecor_unref (*WAYLAND_libdecor_unref)
 #define libdecor_new (*WAYLAND_libdecor_new)