SDL: fix build of testmouse.c

SDL Commits
1 
From 62b41f61d4e740f90abd0c82b7ce1a166342c777 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Sat, 13 Nov 2021 21:29:50 +0300
Subject: [PATCH] fix build of testmouse.c

---
 test/testmouse.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/test/testmouse.c b/test/testmouse.c
index 65e7a3b8f6..facc74c60e 100644
--- a/test/testmouse.c
+++ b/test/testmouse.c
@@ -16,6 +16,8 @@
 #include <emscripten/emscripten.h>
 #endif
 
+#include <stdlib.h> /* exit() */
+
 #ifdef __IPHONEOS__
 #define SCREEN_WIDTH    320
 #define SCREEN_HEIGHT   480
@@ -27,10 +29,8 @@
 static SDL_Window *window;
 static SDL_Renderer *renderer;
 
-typedef struct Line Line;
-
-typedef struct Line {
-    Line *next;
+typedef struct _Line {
+    struct _Line *next;
 
     int x1, y1, x2, y2;
     Uint8 r, g, b;