Hi Vadim,
For generating C code for fmincon (or lsqnonlin, etc.) via MATLAB Coder, we require that you use the optimoptions function to set options. See the requirements in this documentation page.
Also, an important note is that only the SQP algorithm of fmincon is supported for C code generation.
The equivalent code for your example is as follows
optionsNLP = optimoptions('fmincon','Algorithm','sqp','SpecifyObjectiveGradient', false, ...
'CheckGradients', false, 'Display', 'iter', 'StepTolerance', 1e-9, 'FunctionTolerance', 1e-9, ...
'ConstraintTolerance', 1e-9, 'MaxFunctionEvaluations', 300, 'DiffMinChange', 1e-5);
