integrate working fullscreen patch from reddit

thanks /u/leo60228!

src/pc/gfx/gfx_sdl2.c

@@ -21,6 +21,8 @@
 
 #include "src/pc/controller/controller_keyboard.h"
 
+#include "src/pc/configfile.h"
+
 static SDL_Window *wnd;
 static int inverted_scancode_table[512];
 
@@ -86,6 +88,10 @@ static void gfx_sdl_init(void) {
     
     wnd = SDL_CreateWindow("Super Mario 64 PC-Port", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
             DESIRED_SCREEN_WIDTH, DESIRED_SCREEN_HEIGHT, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);
+
+    if (configFullscreen) {
+      SDL_SetWindowFullscreen(wnd, SDL_WINDOW_FULLSCREEN_DESKTOP);
+    }
     
     SDL_GL_CreateContext(wnd);
     SDL_GL_SetSwapInterval(2); // TODO 0, 1 or 2 or remove this line
@@ -180,4 +186,4 @@ struct GfxWindowManagerAPI gfx_sdl = {
     gfx_sdl_swap_buffers_begin,
     gfx_sdl_swap_buffers_end,
     gfx_sdl_get_time
-};
+};