Is it simulation and/or there is some analytical procedure to calculate them?
The analytical process of what limit the aircraft SHOULD be capable of takes place in the Design Engineer's office.
Test pilots must then DEMONSTRATE, in actual Cross-Wind conditions that the aircraft is capable of meeting the demands of the actual Cross-Wind during the test.
If, for example, the aircraft was capable of a 40 Kt Cross-Wind in theory, but the most that the Test Pilot could find was 35 Kt, the AFM would state "Maximum Demonstrated Cross-Wind = 35 Knots". (Seen that statement before?)
Regards,
Old Smokey