2.26.1 release candidate 1 for AmigaOS 4

AmigaOS 4 -specific changes:

• Compile with GCC 11.2
• Fix shaped window alpha bitmap creation
• Enable virtual joysticks
• Add a workaround for game controller detection (AmigaOS 4 GUIDs are unfortunately broken)
• Add 2in1 game controller
• Update installer: delete old libSDL2.so soft links