SDL_image: cmake: disable SDLIMAGE_(AVIF|JPG|PNG)_SAVE when backends are not available

SDL Commits
1 
From 86256318e0cadaf6cb92e49c4ac01a2bc3bd69be Mon Sep 17 00:00:00 2001
From: Anonymous Maarten <[EMAIL REDACTED]>
Date: Sun, 13 Apr 2025 00:35:10 +0200
Subject: [PATCH] cmake: disable SDLIMAGE_(AVIF|JPG|PNG)_SAVE when backends are
 not available

---
 CMakeLists.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index faa7778b..97401c71 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -569,6 +569,9 @@ if(SDLIMAGE_AVIF)
         else()
             target_link_libraries(${sdl3_image_target_name} PRIVATE avif)
         endif()
+    else()
+        # Variable is used by test suite
+        set(SDLIMAGE_AVIF_SAVE OFF)
     endif()
 endif()
 
@@ -647,6 +650,9 @@ if(SDLIMAGE_JPG)
             LOAD_JPG
             SDL_IMAGE_SAVE_JPG=$<BOOL:${SDLIMAGE_JPG_SAVE}>
         )
+    else()
+        # Variable is used by test suite
+        set(SDLIMAGE_JPG_SAVE OFF)
     endif()
 endif()
 
@@ -827,6 +833,9 @@ if(SDLIMAGE_PNG)
             LOAD_PNG
             SDL_IMAGE_SAVE_PNG=$<BOOL:${SDLIMAGE_PNG_SAVE}>
         )
+    else()
+        # Variable is used by test suite
+        set(SDLIMAGE_PNG_SAVE OFF)
     endif()
 endif()