Partially revert 1eb1cc5e5b: it broke the Windows build.

Go back to using SDL2 in front of SDL2 header includes.

src/wx-main.cc

@@ -1,5 +1,5 @@
 #include "wx-app.h"
-#include <SDL.h>
+#include <SDL2/SDL.h>
 
 extern "C"
 {

src/wx-sdl2-display-win.c

@@ -1,5 +1,5 @@
 #define  _WIN32_WINNT 0x0501
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include "video.h"
 #include "wx-sdl2-video.h"
 #include "wx-utils.h"

src/wx-sdl2-display.c

@@ -1,4 +1,4 @@
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include "video.h"
 #include "wx-sdl2-video.h"
 #include "wx-utils.h"

src/wx-sdl2-joystick.c

@@ -1,6 +1,6 @@
 #include <stdlib.h>
 #include <math.h>
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include "ibm.h"
 #include "device.h"
 #include "gameport.h"

src/wx-sdl2-mouse.c

@@ -1,4 +1,4 @@
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include <string.h>
 #include "plat-mouse.h"
 

src/wx-sdl2-status.c

@@ -1,4 +1,4 @@
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include "video.h"
 #include "wx-sdl2.h"
 #include "wx-sdl2-video.h"

src/wx-sdl2-video-gl3.c

@@ -1,8 +1,8 @@
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #define BITMAP WINDOWS_BITMAP
-#include <SDL_opengl.h>
+#include <SDL2/SDL_opengl.h>
 #if SDL_VERSION_ATLEAST(2, 0, 4)
-#include <SDL_opengl_glext.h>
+#include <SDL2/SDL_opengl_glext.h>
 #endif
 #undef BITMAP
 #include "wx-sdl2-glw.h"

src/wx-sdl2-video-renderer.c

@@ -1,4 +1,4 @@
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include <stdint.h>
 #include <string.h>
 #include <stdio.h>

src/wx-sdl2-video.c

@@ -1,4 +1,4 @@
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>

src/wx-sdl2.c

@@ -1,6 +1,6 @@
 #include "wx-sdl2.h"
 
-#include <SDL.h>
+#include <SDL2/SDL.h>
 #include <wx/defs.h>
 
 #ifdef __WINDOWS__