pub type LLVMDiagnosticHandler = Option<extern "C" fn(arg1: LLVMDiagnosticInfoRef, arg2: *mut c_void)>;
enum LLVMDiagnosticHandler { None, Some(extern "C" fn(_: *mut LLVMDiagnosticInfo, _: *mut c_void)), }
No value.
Some value of type T.
T