SDL: Fixed compile warning on gcc 11 (c183b)

SDL Commits
1 
From c183b81fc9750f1f23e905ee38756e330c40117a Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Thu, 19 May 2022 01:23:24 -0700
Subject: [PATCH] Fixed compile warning on gcc 11

---
 src/video/SDL_video.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/video/SDL_video.c b/src/video/SDL_video.c
index d6372435bdf..fa926e51d57 100644
--- a/src/video/SDL_video.c
+++ b/src/video/SDL_video.c
@@ -4348,7 +4348,7 @@ SDL_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
         return SDL_SetError("Invalid number of buttons");
     }
 
-    SDL_AtomicIncRef(&SDL_messagebox_count);
+    (void)SDL_AtomicIncRef(&SDL_messagebox_count);
 
     current_window = SDL_GetKeyboardFocus();
     relative_mode = SDL_GetRelativeMouseMode();
@@ -4456,7 +4456,7 @@ SDL_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
         }
     }
 
-    SDL_AtomicDecRef(&SDL_messagebox_count);
+    (void)SDL_AtomicDecRef(&SDL_messagebox_count);
 
     if (current_window) {
         SDL_RaiseWindow(current_window);