slightly more reproducible builds

slightly more reproducible builds

in vop templates, (:constant <type>) eventually boiled down to a TYPEP
test.  For (:constant fixnum) in the cross-compiler, this is not right,
because the typep test runs on the host.  Use SB!XC:TYPEP instead, which
means making sure that types are available to the cross-compiler (using
DEF!TYPE instead of DEFTYPE).  Tested on x86-64; one issue on ppc fixed
blindly.