18.104.22.168: 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.