cmake: improve check of APNG feature availability

Author: adriweb

gui/qt/CMakeLists.txt

@@ -285,8 +285,15 @@ endif()
 
 find_package(PNG QUIET)
 if(PNG_FOUND)
-    target_compile_definitions(CEmu PRIVATE "PNG_SUPPORT")
-    target_link_libraries(CEmu PRIVATE PNG::PNG)
+    include(CheckSymbolExists)
+    set(CMAKE_REQUIRED_INCLUDES ${PNG_INCLUDE_DIRS})
+    check_symbol_exists(PNG_WRITE_APNG_SUPPORTED "png.h" HAVE_PROPER_APNG_LIB)
+    if(HAVE_PROPER_APNG_LIB)
+        target_compile_definitions(CEmu PRIVATE "PNG_SUPPORT")
+        target_link_libraries(CEmu PRIVATE PNG::PNG)
+    else()
+        message(WARNING "The LibPNG found does not seem to support APNG. APNG capture will not be available")
+    endif()
 else()
     message(WARNING "No LibPNG found! APNG capture will not be available")
 endif()