got rid of :SB-CONSTRAIN-FLOAT-TYPE as a separate target
*FEATURES* option controlling the build (instead
hardwiring it to always be on)
removed some CROSS-FLOAT-INFINITY-KLUDGE SB-XC-HOST
conditionalization from srctran..
..Defining support functions is ok, as long as we don't
actually execute the paths which mess with floating
..Stuff which doesn't use floats should be OK, too: ASH,
LOGNOT, LOGAND, LOGIOR, LOGXOR..
..Things which work with integers exclusively (not floats)
should be safe.