Support 128bit numbers

[bjorn3]

Blocked on bytecodealliance/cranelift#795

[bjorn3]

128bit multiplication is currently failing, because checked binops are not yet implemented for 64bit integers.

Note to self

llvm:

a: lo=353985398 hi=0
b: lo=932490 hi=0
result: lo=-1867753060 hi=0
n: lo=-1 hi=-1
d: lo=932490 hi=0
r: lo=1048575 hi=0
s: lo=-1 hi=-1
[..]

clif:

a: lo=353985398 hi=0
b: lo=932490 hi=0
result: lo=-1867753060 hi=0
n: lo=-1 hi=-1
d: lo=932490 hi=0
r: lo=1048575 hi=0
s: lo=-1 hi=-1
d & s as $ty: lo=932490 hi=0

Edit: #646 implemented checked binops, making 128bit multiplication succeed 🎉

[bjorn3]

Switched to use my own fork of cranelift. This means that we don't have to wait for bytecodealliance/cranelift#795 to land.

[bjorn3]

Going to merge this, as it blocks compilation of many crates.