When an FPU exception is masked the appropriate flag in the status
word will still be set, so get_fpu_code() should mask the exception
flags in the status word with the exception flags in the control word.

ExceptionAddress isn't the same as EIP for FPU exceptions, since the
exception will be thrown on the next FPU instruction, rather than the
instruction that caused the exception.

Also fix the compiler warnings produced by this change.