comp and extended are additional types of the x87 floating point processor. They are only supported on targets where such fpu unit is supported.
The have_* are mostly set in the compiler (and the fpdoc parser has to set them to emulate that), they can't be turned on or off anyway.
Since D4 and FPC 2.0.0 there is a new type, int64 that can be used as replacement, and the use of comp is discouraged.