If I remember correctly, the host environment, i.e. vbcc itself, uses the OS math libraries. If your target math environment is different, keep an eye on precision. Constants and operations generated by the compiler may round differently than bits generated at run time. If you need consistency, test your host environment, and then set the FPU rounding mode appropriatly at program startup.
Edit: You could alternatively build host-specific vbcc executables--one for libs, one for 68881, one for 68040, etc--and then match host to target with e.g. -fpu=foo.
