compatibility of strerror_r on different platforms

Question

I am trying to use strerror_r() function for getting error string corresponding to an error code and I am targeting BSD and Linux platforms, but the man page of strerror_r() says:

int strerror_r(int errnum, char *buf, size_t buflen);
                   /* XSI-compliant */

char *strerror_r(int errnum, char *buf, size_t buflen);
                   /* GNU-specific */

So I am not sure of it's compatibility(the XSI compliancy and GNU specific compliancy) on different platforms, I would appreciate if you could help me telling which platforms is it compatible on ? On which platforms I get which version out of the above ?