Function moq_qlog_supported 

#[unsafe(no_mangle)]
pub extern "C" fn moq_qlog_supported() -> bool

Whether this build can capture qlog traces.

Capture is compile-time optional. moq_client_set_quic_qlog accepts a directory either way, but dialing fails when the support is absent, so a caller offering the knob should hide it rather than surface an option that cannot work.