`@floatToInt` now has safety-checked undefined behavior

when the integer part does not fit in the destination integer type

 * Also fix incorrect safety triggered for integer casting an
   `i32` to a `u7`. closes #1138
 * adds compiler-rt function: `__floatuntidf`
c7804277bfAndrew Kelley committed on 6/19/2018, 8:06:10 PMparent0b92d68
12 files changedLine totals unavailable