mc88100	Rewrite mul.  Write addmul, submul.
vax	Write lshift, rshift (using ashq)?
r4000	Write addmul, submul (trivial mod of r3000 code).
mc680x0	Fix syntax for all targets.
i386	Fix syntax for all targets.

arm,clipper,cray,i860,i960,mc88110,powerpc,pyramid,romp,sparc9,transputer,tron,we32100

PARI has some nice functions for udiv_qrnnd, but they are large
and not always optimal.  We should use some of their ideas, though.
