Add missing _cast_uitofp/fptoui, setzero and min_varying functions

This commit fixes several compfails (listed in fail_db.txt). No new runfails were noticed, but there are load/store functions which were compfailing and now might be runfailing with a segfault due to unaligned memory access.
I prefer (i?",":"") to be spelled ( i != 0 ? ...
Using implicit != 0 is good for pointers, but for integers it's better to spell it out.