Bitcast to values represented with LLVM structs cause a compiler crash

[vdka]

Bitcast code needs a re-write. Perhaps casting can be unified in the LLVM backend.
The only difference between cast and bitcast is that bitcast requires equally sized types & Floating Pointer <-> Integer conversions are handled differently.
Note bad IR gen in the following case also:

A :: struct {
    a: rawptr
}
main :: fn() -> void {
    x : rawptr = nil
    a := bitcast(A) x
}