Add uadd_overflow_trap (#5123)

Add a new instruction uadd_overflow_trap, which is a fused version of iadd_ifcout and trapif. Adding this instruction removes a dependency on the iflags type, and would allow us to move closer to removing it entirely.

The instruction is defined for the i32 and i64 types only, and is currently only used in the legalization of heap_addr.

cranelift/codegen/src/write.rs

@@ -418,6 +418,7 @@ pub fn write_operands(w: &mut dyn Write, dfg: &DataFlowGraph, inst: Inst) -> fmt
         }
         IntCompare { cond, args, .. } => write!(w, " {} {}, {}", cond, args[0], args[1]),
         IntCompareImm { cond, arg, imm, .. } => write!(w, " {} {}, {}", cond, arg, imm),
+        IntAddTrap { args, code, .. } => write!(w, " {}, {}, {}", args[0], args[1], code),
         FloatCompare { cond, args, .. } => write!(w, " {} {}, {}", cond, args[0], args[1]),
         Jump {
             destination,