1.0.28.54: more principled approach to complex dumping in the xc

  Christophe points out that (UPGRADED-COMPLEX-PART-TYPE 'DOUBLE-FLOAT)
  can be REAL on some hosts, in which case the host will happily
  agree that (TYPEP #C(2 2) '(COMPLEX DOUBLE-FLOAT)) is true... etc.

  So in the cross compiler look at the type of the parts of the
  complex, and refuse to dump it if it doesn't look like something we
  can handle correctly.