* try some macos travis stuff
* put c in the link libs for macos since we always link with libSystem
* for non-native targets on macos, allow runtime symbol resolution
- it's causing an infinite loop in LLD.
* for macos, always build compiler_rt and turn on LinkOnce because
compiler_rt on darwin is missing some stuff.
* add u3, u4, u5, u6, u7 and i3, i4, i5, i6, i7
* shift operations shift amount parameter type is
integer with log2 bit width of other param
- This enforces not violating undefined behavior on
shift amount >= bit width with the type system
* clean up math.log, math.ln, math.log2, math.log10
closes#403
