Cranelift: Implement iadd_cout on x64 for 32- and 64-bit integers (#5285)

* Split the `iadd_cout` runtests by type

* Implement `iadd_cout` for 32- and 64-bit values on x64

* Delete trailing whitespace in `riscv/lower.isle`

cranelift/codegen/src/isa/x64/inst.isle

@@ -2124,6 +2124,15 @@
          (MInst.Setcc cc dst)
          dst)))
 
+;; Helper for creating `MInst.Setcc` instructions, when the flags producer will
+;; also return a value.
+(decl x64_setcc_paired (CC) ConsumesFlags)
+(rule (x64_setcc_paired cc)
+      (let ((dst WritableGpr (temp_writable_gpr)))
+        (ConsumesFlags.ConsumesFlagsReturnsResultWithProducer
+         (MInst.Setcc cc dst)
+         dst)))
+
 ;; Helper for creating `MInst.XmmRmR` instructions.
 (decl xmm_rm_r (Type SseOpcode Xmm XmmMem) Xmm)
 (rule (xmm_rm_r ty op src1 src2)