Compilation fixes/improvements for core and webOS support

[cscd98]

• Makes vulkan optional and enabled by default
• Disable QT etc. not needed for a libretro core
• Fixes compilation errors with modern GCC 14
• Add webOS as a platform

Please test! (not the webOS bit)

I've assumed these are not needed. If I'm wrong let me know:

if(ENABLE_LIBRETRO)
    set(ENABLE_QT OFF)
    set(ENABLE_QT_UPDATER OFF)
    set(ENABLE_DEDICATED_ROOM OFF)
    set(ENABLE_WEB_SERVICE OFF)
    set(ENABLE_SCRIPTING OFF)
    set(ENABLE_CUBEB OFF)
    set(ENABLE_OPENAL OFF)
    set(ENABLE_TESTS OFF)
    set(CITRA_ENABLE_BUNDLE_TARGET OFF)
endif()